Modicon Modbus Plus Network Planning and Installation

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Modicon Modbus Plus Network Planning and Installation Guide890 USE 100 00 Version 6.0

2 890 USE 100 00 November 2004

890 USE 100 00 November 2004 3

Table of Contents

Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

About the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Chapter 1 Introducing the Modbus Plus Network . . . . . . . . . . . . . . . . . . . 11Introducing the Modbus Plus Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Network Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Overview of the Logical Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Overview of the Physical Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Major Components of the Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

How Nodes Access the Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Error Checking and Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Designing for Process Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Designing for Deterministic I/O Servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Using Peer Cop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Expanding the Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Joining Modbus Plus Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Bridging Modbus Plus and Serial Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Chapter 2 Elements of Network Planning . . . . . . . . . . . . . . . . . . . . . . . . . 47An Overview of Network Planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Defining the Network Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Defining the Network Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Chapter 3 Estimating Network Performance . . . . . . . . . . . . . . . . . . . . . . . 55Estimating Network Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Factors for Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

How Devices Interact on the Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Factors That Affect Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Communication Paths and Queuing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Reading and Writing with the MSTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

A Sample MSTR Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Getting and Clearing Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Reading and Writing Global Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Loading Effects in Your Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

4 890 USE 100 00 November 2004

Predicting Token Rotation Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Formula for Calculating Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Predicting MSTR Response Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Estimating Throughput (With MSTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Estimating Throughput (With Peer Cop) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Predicting Node Dropout Latency Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Estimating Latency for a Small Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Estimating Latency for a Large Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Planning for Ring Join Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Precautions for Hot Standby Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Guidelines for a Single Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Guidelines for Multiple Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Sample Communications Across Networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

A Summary of Network Planning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Chapter 4 Documenting the Network Layout . . . . . . . . . . . . . . . . . . . . . 101Documenting Your Network Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Worksheets for Network Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Defining Your Node Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Topology Planning Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Estimating Cable Lengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Reviewing Your Topology Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Detailing the Network Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Network Planning Worksheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Cable Routing Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Materials Summary Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Chapter 5 Installing the Network Cable. . . . . . . . . . . . . . . . . . . . . . . . . . 121Overview of the Cable Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Tools and Test Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Routing the Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Mounting the Taps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Connecting the Trunk Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

Connecting the Drop Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

Labeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

Checking the Cable Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Chapter 6 Connecting an RR85 Repeater . . . . . . . . . . . . . . . . . . . . . . . . 137Mounting Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Mounting Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Installing the Repeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Reading the Network Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

RR85 Repeater Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

890 USE 100 00 November 2004 5

Chapter 7 Connecting a BP85 Bridge Plus . . . . . . . . . . . . . . . . . . . . . . . 145Mounting Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Dimensions (Panel/Shelf Models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

Dimensions (Rack Mount Model) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

Setting the Modbus Plus Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Connecting the Power Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Connecting the Network Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Applying Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Reading the Network Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

Attaching Port Identification Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

BP85 Bridge Plus Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Appendix A Modbus Plus Transaction Elements . . . . . . . . . . . . . . . . . . . . 161Transaction Timing Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

The Message Format HDLC Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

The Message Format MAC Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

The Message Format LLC Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

Appendix B Message Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171The Modbus Plus Message Routing Path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Modbus Address Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Controller Bridge Mode Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Bridge Multiplexer Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

Appendix C Planning Worksheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Appendix D Installing Custom Cable Systems . . . . . . . . . . . . . . . . . . . . . . 195Installing the Network Cable System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

Tools and Test Equipment Required. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

Routing the Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Installing Connectors on Dual-Cable Runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

Installing Connectors with the Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

Installing Connectors without the Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

Labeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

Checking the Cable Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

6 890 USE 100 00 November 2004

890 USE 100 00 November 2004 7

ßSafety Information

Important Information

NOTICE Read these instructions carefully, and look at the equipment to become familiar with

the device before trying to install, operate, or maintain it. The following special

messages may appear throughout this documentation or on the equipment to warn

of potential hazards or to call attention to information that clarifies or simplifies a

procedure.

The addition of this symbol to a Danger or Warning safety label indicates

that an electrical hazard exists, which will result in personal injury if the

instructions are not followed.

This is the safety alert symbol. It is used to alert you to potential personal

injury hazards. Obey all safety messages that follow this symbol to avoid

possible injury or death.

DANGER indicates an imminently hazardous situation, which, if not avoided, will

result in death, serious injury, or equipment damage.

DANGER

WARNINGWARNING indicates a potentially hazardous situation, which, if not avoided, can result

in death, serious injury, or equipment damage.

CAUTIONCAUTION indicates a potentially hazardous situation, which, if not avoided, can result

in injury or equipment damage.

Safety Information

8 890 USE 100 00 November 2004

PLEASE NOTE Electrical equipment should be serviced only by qualified personnel. No responsi-

bility is assumed by Schneider Electric for any consequences arising out of the use

of this material. This document is not intended as an instruction manual for untrained

persons.

© 2004 Schneider Electric. All Rights Reserved.

890 USE 100 00 November 2004 9

About the Book

At a Glance

Document Scope Modbus Plus is a local area network system for industrial control applications.

Networked devices can exchange messages for the control and monitoring of

processes at remote locations in the industrial plant.

Modicon products supporting Modbus Plus communication include programmable

controllers and network adapters. The network is also supported by a variety of

products from other manufacturers.

Each Modicon controller can connect to Modbus Plus directly from a port on its front

panel. Additional networks can be accessed through Network Option Modules

(NOMís) installed in the common backplane.

The network also provides an efficient means for servicing input/output subsystems.

Modicon Modbus Plus Distributed I/O (DIO) Drop Adapters and Terminal Block I/O

(TIO) modules can be placed at remote I/O sites to allow the application to control

field devices over the network link.

Validity Note The data and illustrations found in this book are not binding. We reserve the right to

modify our products in line with our policy of continuous product development. The

information in this document is subject to change without notice and should not be

construed as a commitment by Schneider Electric.

About the Book

10 890 USE 100 00 November 2004

Related Documents

Product Related

Warnings

Schneider Electric assumes no responsibility for any errors that may appear in this

document. If you have any suggestions for improvements or amendments or have

found errors in this publication, please notify us.

No part of this document may be reproduced in any form or by any means, electronic

or mechanical, including photocopying, without express written permission of

Schneider Electric.

All pertinent state, regional, and local safety regulations must be observed when

installing and using this product. For reasons of safety and to ensure compliance

with documented system data, only the manufacturer should perform repairs to

components.

When controllers are used for applications with technical safety requirements,

please follow the relevant instructions.

Failure to use Schneider Electric software or approved software with our hardware

products may result in improper operating results.

Failure to observe this product related warning can result in injury or equipment

damage.

User Comments We welcome your comments about this document. You can reach us by e-mail at

[email protected]

Title of Documentation Reference Number

Modicon Quantum Automation series Hardware Reference Guide 840 USE 100 00

Modicon Ladder Logic Block Library User Guide 840 USE 101 00

Modicon Modbus Plus Network I/O Servicing Guide 840 USE 104 00

Modicon IBM Host Based Devices Userís Guide 840 USE 102 00

Modicon Modbus Plus Network BM85 Bridge Multiplexer Userís Guide 840 USE 103 00

Modicon DEC Host Based Devices Userís Guide GM-HBDS-002

Modicon Modbus Protocol Reference Guide PI-MBUS-300

890 USE 100 00 November 2004 11

1Introducing the Modbus Plus Network

At a Glance

Overview This chapter provides an introduction to the Modbus Plus Network.

What's in this Chapter?

This chapter contains the following topics:

Topic Page

Introducing the Modbus Plus Network 12

Network Terminology 14

Overview of the Logical Network 16

Overview of the Physical Network 17

Major Components of the Network 20

How Nodes Access the Network 28

Error Checking and Recovery 30

Designing for Process Speed 31

Designing for Deterministic I/O Servicing 32

Using Peer Cop 33

Expanding the Network 36

Joining Modbus Plus Networks 39

Bridging Modbus Plus and Serial Devices 42

Introducing the Modbus Plus Network

12 890 USE 100 00 November 2004


Overview Modbus Plus is a local area network system for industrial control applications.

Networked devices can exchange messages for the control and monitoring of

processes at remote locations in the industrial plant.

Schneider Electric products supporting Modbus Plus communication include

programmable controllers and network adapters. The network is also supported by

a variety of products from other manufacturers.

Each controller can connect to Modbus Plus directly from a port on its front panel.

Additional networks can be accessed through network option modules (NOMs)

installed in the common backplane.

The network also provides an efficient means for servicing input/output subsystems.

Modbus Plus distributed I/O (DIO) drop adapters and terminal bock I/O (TIO)

modules can be placed at remote I/O sites to allow the application to control field

devices over the network link.

Extending the Network

Each network supports up to 64 addressable node devices. Up to 32 nodes can

connect directly to the network cable over a length of 1500 ft (450 m). Repeaters can

extend the cable distance to its maximum of 6000 ft (1800 m) and the node count to

its maximum of 64. Fiber optic repeaters are available for longer distances.


890 USE 100 00 November 2004 13

Bridging Networks

Multiple networks can be joined through Bridge Plus devices. Messages originated

on one network are routed through one or more bridges to a destination on another

network. Bridges are applicable to networks in which fully deterministic timing of I/O

processes is not a requirement. In a network requiring deterministic I/O timing,

messages for DIO/TIO nodes are passed on that network only, and do not pass

through bridges.

Modbus and custom RS232/RS485 serial devices can access Modbus Plus through

bridge multiplexers. Each bridge multiplexer provides four configurable serial ports.

A serial device can communicate with Modbus Plus networked devices, as well as

with other devices at the serial ports.

The following figure shows four Modbus Plus networks. A repeater extends the

cable for network A. networks A and B are joined by a Bridge Plus.

Networks C and D handle I/O processes. DIO drop adapters and terminal block I/O

modules service the I/O field devices at each site.

CPU CPURR85

repeater

BP85bridgeplus

BM85bridge

multiplexer

host devicenetworkadapter

user

interfaceModbus or custom

serial devices

network A

network B

network C

network D

TIO

TIOTIOI/O

modules

I/O

modulesP

S

C

PU

N

OM

N

OM

Up to 64nodestotal

up to 64nodestotal

up to 64nodestotal

up to 64nodestotal

hostcomputer

D

IO

I/O

modules

D

IO


14 890 USE 100 00 November 2004

Network Terminology

Network A network is the grouping of nodes on a common signal path that is accessed by the

passing of a token. It consists of one or more cable sections. For example, all of the

nodes in the graphic below are on a network.

Section A section is a series of nodes that are joined only by cable segments. The sectionís

signal path does not pass through any kind of node device. Sections are all part of

one network, sharing the same token and address sequence. In the graphic above,

the repeater joins two sections. Each section can be up to1500 ft (450 m) long and

can contain up to 32 physical node connections.

Cable Segment A cable segment is a single length of trunk cable between two taps. Taps are

passive devices that provide connections for the trunk cable segments. In the

graphic above, the cable connection between the nodes at addresses 10 and 5 is

through one cable segment. Another cable segment connects nodes 5 and 64.

On dual-cable networks, two cable segments run in parallel between pairs of nodes.

Node A node is any device that is physically connected to the Modbus Plus cable. The

graphic above shows a network with 7 node devices. The term applies to any device,

whether it is addressable or not. Some nodes, like programmable controllers, have

addresses and can serve as sources or destinations for messages. The bridge plus

is a separately addressable node on each of its 2 networks. The repeater is a node

on each of 2 sections, but has no address, serving only to extend the network.

Section

cablesegment

devicesare on twosections of

one network

node node node

node nodenode

node

repeater

node

10

node

5

node

64

node

14node

23

node

2


890 USE 100 00 November 2004 15

Token A token is a grouping of bits that is passed in sequence from one device to another

on a single network, to grant access for sending messages. If 2 networks are joined

by a bridge plus, each network has its own token that is passed only among the

devices on that network.

DIO Network A distributed I/O (DIO) network is a Modbus Plus network designed primarily for

servicing I/O field devices in the application. In its minimum configuration, a DIO

network consists of one controller (CPU) and one or more drops located at remote

sites near to the field devices.

Each drop consists of a DIO drop adapter installed in a backplane with I/O modules

or a terminal block I/O (TIO) module.

In the figure below, one DIO network contains the CPU, a DIO adapter, and a TIO

module. Two other DIO networks consist of network option modules (NOMs) with

DIO drop adapters and TIO modules.

Details for designing a Modbus Plus network, which is intended primarily for I/O

servicing, are located in the Modbus Plus Network I/O Servicing Guide

(840USE10400).

TIOI/O

modulesP

S

C

PU

N

OM

N

OM

up to 64nodestotal

up to 64nodestotal

I/O

modules

D

IO

TIOI/O

modules

D

IO

TIOI/O

modules

D

IO

up to 64nodestotal


16 890 USE 100 00 November 2004

Overview of the Logical Network

Overview Network nodes are identified by addresses assigned by the user. Each nodeís

address is independent of its physical site location. Addresses are within the range

of 1 to 64 decimal, and do not have to be sequential. Duplicate addresses are not

allowed.

Network nodes function as peer members of a logical ring, gaining access to the

network upon receipt of a token frame. The token is a grouping of bits that is passed

in a rotating address sequence from one node to another. Each network maintains

its own token rotation sequence independently of the other networks. Where

multiple networks are joined by bridges, the token is not passed through the bridge

device.

While holding the token, a node initiates message transactions with other nodes.

Each message contains routing fields that define its source and destination,

including its routing path through bridges to a node on a remote network.

When passing the token, a node can write into a global database that is broadcast

to all nodes on the network. Global data is transmitted as a field within the token

frame. Other nodes monitor the token pass and can extract the global data if they

have been programmed to do so. Use of the global database allows rapid updating

of alarms, setpoints, and other data. Each network maintains its own global

database, as the token is not passed through a bridge to another network.

The figure below shows the token sequences in two networks joined by a bridge

plus.

node

network 1

token sequence: 2 - 5 - 10 - 12 - 22 - 2. . .

node node node

bridgeplus

node nodenode node

network 2

token sequence: 4 - 5 - 9 - 10 - 24 - 4. . .

2

5

12

10

22

24

10

4

5

9


890 USE 100 00 November 2004 17

Overview of the Physical Network

Overview The network bus consists of twisted-pair shielded cable that is run in a direct path

between successive nodes. The two data lines in the cable are not sensitive to

polarity; however, a standard wiring convention is followed in this guide to facilitate

maintenance.

The network consists of one or more cable sections, with any section supporting up

to 32 nodes at a maximum cable distance of 1500 ft (450 m). Sections can be joined

by repeaters to extend the network length and support up to 64 nodes.

Minimum/

Maximum Cable

Length

The minimum cable length between any pair of nodes must be at least 10 ft (3 m).

The maximum cable length between two nodes is the same as the maximum section

length of 1500 ft (450 m).

Dual Cable On dual-cable networks, the cables are known as cable A and cable B. Each cable

can be up to 1500 ft (450 m) long, measured between the two extreme end devices

on a cable section. The difference in length between cables A and B must not

exceed 500 ft (150 m),measured between any pair of nodes on the cable section.


18 890 USE 100 00 November 2004

Tap Devices Nodes are connected to the cable by means of a tap device, supplied by Schneider

Electric. This provides through connections for the network trunk cable, drop

connections for the cable to the node device, and a grounding terminal.

The tap also contains a resistive termination that is connected by two internal

jumpers. The tap at each end of a cable section requires both of its jumpers to be

connected to prevent signal reflections. All of the taps that are inline on the cable

section require their jumpers to be removed (open).

The figure below illustrates a tap at an inline site. Two lengths of trunk cable are

installed. When a tap is installed at the end site of a cable section, only one length

of trunk cable is routed to the tap. It can enter at either side of the tap. The jumpers

are connected to the signal pins at the opposite side of the tap to provide the network

termination.

1 network trunk cable

2 cable tie

3 termination jumpers (2)

4 drop cable to node

5 ground wire

tap shown with cover open

end sites: connected to pins at opposite side from trunk able entryinline sites: open

11

2

3

4 5


890 USE 100 00 November 2004 19

The next two figures summarize the layout for one section of a network

up to 32 nodes max. 1500 ft (450 m) cable max.

10 ft (3 m) cable min.

endnode

endnode

inlinenode

inlinenode

jumpers connected jumpers disconnected

up to 32 nodes max. 1500 ft (450 m) cable max.500 ft (150 m) max. difference between cables A and B

measured between any pair of nodes


cable A

cable B

endnode

endnode

inlinenode

inlinenode

jumpers connected jumpers disconnected


20 890 USE 100 00 November 2004

Major Components of the Network

Programmable Controllers

Schneider Electric controllers connect directly to the network bus cable through a

dedicated Modbus Plus communication port that is located on the controller

assembly. The port allows the controller to communicate with other networked

controllers, host computers with network adapters, and DIO drops.

Controller models are available for single-cable and dual-cable network layouts.

Contact your Schneider Electric distributor for information about models and part

numbers.

Each controller functions as a peer on the network, receiving and passing tokens

and messages. The user application program can access registers in the local

controller and in the other networked controllers.

Types of Communication

Three types of communication are available to the application program for

exchanging messages between networked nodes:

! The MSTR function block can be used for transferring, reading and clearing

statistics, and accessing the networkís global database. The MSTR is a general

function for transacting messages with any type of networked node. It is

programmed into the user logic program of the controller.

! Peer cop transfers can be used to move data both globally and with specific

nodes. Such transfers are specified in the controllerís peer cop table during its

initial configuration.

! Distributed I/O transfers can be used to move data with DIO drop adapter nodes.

Such transfers are specified in the controllerís DIO map table during its initial

configuration.

Hot Standby

Configurations

When two controllers are connected in a redundant (hot standby) configuration,

each controller is seen as a separate address on the network. This use of dual

addressing allows both controllers to be fully accessed for programming and

statistics. If a transfer occurs to the standby controller, the primary and standby

addresses are exchanged, maintaining consistent addressing within the application.

Note: The address exchange can cause a momentary delay in communication with

the new primary unit while it assumes its place in the network token rotation

sequence. This can be a significant factor in the timing of processes using

redundant controllers. The application should provide retry capabilities in the other

nodes to cover this time.


890 USE 100 00 November 2004 21

Network Option Modules

The network option module (NOM) mounts in the backplane with the controller. It

allows the user application program, running in the controller, to communicate with

an additional Modbus Plus network. The additional network can be configured with

controllers, other NOMs, distributed I/O nodes, or a combination of these devices.

One or two NOMs can be mounted in the controller's housing. Power is taken from

the power supply module, which must also be installed in the housing.

Network option modules are available for single-cable and dual-cable network

layouts. Contact your Schneider Electric distributor for information about models

and part numbers.

The figure below is an example of a network option module.

Note: network option modules are available for either single-cable or dual-cable

network layouts. The dual-cable model is shown.

Modbus Plusaddress switches

(on rear)

modbusconnector

Modbus Plusconnectorchannel A

Modbus Plusconnectorchannel B

(Cover Open)


22 890 USE 100 00 November 2004

DIO Drop Adapters

The DIO drop adapter mounts in a housing at a remote site, communicating over the

housing backplane to the siteís I/O modules to service the siteís data requirements.

The adapter includes a built-in power supply that provides operating power for the I/

O modules.

DIO adapters are available for single-cable and dual-cable network layouts. Contact

your Schneider Electric distributor for information about models and part numbers.

The figure below shows the front view of a typical DIO drop adapter. Specifications

are provided in the Quantum Automation Series Hardware Reference Guide

(840USE10000).

Available

Backplanes for

DIO Applications

Schneider Electric backplanes are available in sizes from 2 to 16 slots. The DIO drop

adapter module occupies one slot, and contains a power supply that furnishes

operating power to the housing for I/O modules. The supplyís capacity is 3.0 A.

Note: DIO drop adapters are available for either single-cable or dual-cable network

layouts. The dual-cable model is shown.


(on rear)

power/groundterminal strip

Modbus Plusconnectorchannel A

Modbus Plusconnectorchannel B

(cover open)


890 USE 100 00 November 2004 23

Terminal Block I/O (TIO) Modules

Remote sites can be serviced using terminal block (TIO) modules. These compact

modules mount directly to a panel or DIN rail, and provide direct wiring connections

to field devices at the site. TIO modules are available for single-cable layouts only,

and are not applicable for use in dual-cable layouts.

The figure below shows the front view of a typical TIO module. Specifications are in

the Terminal Block I/O Modules Hardware Reference Guide (890USE10400).

Note: TIO modules are available for single-cable layouts only.

Modbus Plusconnector


label forfield wiring

slots forfield wiringconnectors


24 890 USE 100 00 November 2004

Network Adapters for

Host Computers

Adapters are available for connecting host computers to the Modbus Plus network.

The SA85 network adapter connects an IBM AT or compatible product to the

network. The SM85 network adapter connects an IBM personal system/2 or

compatible product using a MicroChannel bus. The SQ85 connects a DEC

MicroVAX II or 3000.

The figure below shows the configuration of an SA85 adapter into an IBM AT-

compatible host computer.

Adapters are supplied complete with the required device driver, a library of C

functions that can be called by the application, a network diagnostic utility, and a set

of sample programs. The Modbus Plus network cable connects to a communications

port on the adapter.

The adapterís device driver responds to a library of NetBios functions that are called

from the application program. These allow sending and receiving data packets,

sending and receiving global data transactions, and monitoring status.

Applications running in the host computer can read and write references at other

nodes. They can also program remote nodes and access the global database.

Note: This graphic is an example of the SA85 and host configuration.

AM-SA85-000

AM-SA85-002

(OR)

Modbus Plus network

single cable

dual cable

devicedriverand

NETBIOSlibrary


890 USE 100 00 November 2004 25

Typical Network Adapter

Applications

Typical network adapter applications include:

! user interfaces

! control, monitoring, and reporting of remote processes

! program load/record/verify operations

! online programming

! bridging between Modbus Plus and other networks

! testing and debugging of application programs

! running network diagnostic programs

Modbus commands received from the Modbus Plus network that are addressed to

the network adapter can be given to tasks running in the computer. Examples

include:

! running a data logging task in the host, accessed by other nodes on the network

! providing virtual registers for remote controllers

Each adapter can be separately configured for its use of memory, interrupts, and

other parameters. This allows flexibility in using multiple adapters in the same host

computer. You can also apply the adapter as a bridge between Modbus Plus and

other networks which may be present, including those which may also be using

NetBIOS.

Information about installing the network adapters, setting their Modbus Plus

parameters, and connecting them to the network, is supplied with the adapters.

BM85 Bridge Multiplexer

The BM85 bridge multiplexer provides connection to Modbus Plus for up to four

kinds of serial devices. Four BM85 models are available. Two of these connect

Modbus devices, or networks of Modbus devices, to the Modbus Plus network. Each

of the Modbus ports can be separately configured to support a Modbus master

device, slave device, or network of slave devices. Port parameters are also

separately configurable.

Two other BM85 models are available for user-defined RS232 or RS485 serial

devices. They include a library of C language functions for creating a user

application program.

Bridge multiplexers are available for single-cable and dual-cable network layouts.


numbers.


26 890 USE 100 00 November 2004

BM85 Bridge Plus

The BP85 bridge plus allows you to connect two Modbus Plus networks. The routing

information in each message allows a node on one network to communicate through

the bridge plus to a destination node on another network. Up to four bridges can be

present in the message path between the source and destination nodes. You can

therefore join up to five Modbus Plus networks along a linear path, with any node

being able to communicate with any other node.

Bridge plus devices are not applicable to Modbus Plus DIO networks because those

networks transfer data messages as part of the token pass. Tokens are not passed

through the bridge plus.

The bridge plus contains two ports for connection to its two networks. It functions as

an addressable node on each of the two networks it joins.It contains two sets of

address switches, for setting its node address on each network. The two addresses

can be set to the same or different values because they are independent of each

other.

Bridge plus models are available for single-cable and dual-cable network layouts.


numbers.

Note: The bridge plus may still be placed on a DIO network to allow non-DIO

messages to be passed to another network. For example, statistical reporting can

be handled between a controller on the DIO link and a network adapter in a host

processor on another network.


890 USE 100 00 November 2004 27

RR85 Repeater The RR85 repeater allows you to place more than 32 nodes on the network and to

increase the cable distance up to an additional 1500 ft (450 m). It functions as an

amplifier and signal conditioner to maintain adequate signal levels between its two

sections of the network. Up to three repeaters may be present in the message path

between the source and destination nodes. You can, therefore, join up to four

sections along a single linear path. Other configurations are possible and are

described later in this chapter.


numbers.

In addition to its use in extending the network, the repeater can be applied in plant

environments that have high levels of electrical interference. Repeaters at key points

in the cable system can help to maintain an excellent signal to noise ratio on the

network.

The repeater is provided with two ports for connection to the two sections. It is

counted as a physical node on each section. The repeater does not have a network

address. It transparently passes tokens and messages as they are received.

When repeaters are used in dual-cable network layouts, one repeater must be

positioned on each cable at the same point (between the same pair of nodes)

as on the other cable. Information is supplied in this book for installing repeaters

(see p. 140).


28 890 USE 100 00 November 2004

How Nodes Access the Network

How Your Applicationís

Layout Affects

Node Access

When the network is initialized, each node becomes aware of the other active

nodes. Each node builds a table identifying the other nodes. Initial ownership of the

token is established, and a token rotation sequence begins. Your choice between

laying out your application as one large network, or as several smaller networks,

affects the timing of the complete token rotation.

For example, tokens are not passed through bridge plus nodes, although messages

can be addressed through bridge plus nodes to destination nodes. You can

therefore construct your networking application as several smaller networks, joined

by bridge plus nodes. The fast token rotation time in each small network allows rapid

transfer of high-priority data, with lower-priority data passing through bridges to

other networks. This facilitates time-critical messaging to nodes that are tightly

linked in an application.

The Token

Rotation Sequence

The token sequence is determined by the node addresses. Token rotation begins at

the networkís lowest-addressed active node, proceeding consecutively through

each higher-addressed node, until the highest-addressed active node receives the

token. That node then passes the token to the lowest one to begin a new rotation.

If a node leaves the network, a new token-passing sequence will be established to

bypass it, typically within 100 milliseconds. If a new node joins, it will be included in

the address sequence, typically within 5 seconds (worst-case time is 15 seconds).

The process of deleting and adding nodes is transparent to the user application.

Where multiple networks are joined by bridges, tokens are not passed through a

bridge device from one network to another. Each network performs its token passing

process independently of the other networks.


890 USE 100 00 November 2004 29

Point to Point Message

Transactions

While a node holds the token, it sends its application messages if it has any to

transmit. Each message can contain up to 100 controller registers (16 - bit words) of

data. The other nodes monitor the network for incoming messages.

When a node receives a message, it sends an immediate acknowledgment to the

originating node. If the message is a request for data, the receiving node will begin

assembling the requested data into a reply message. When the message is ready,

it will be transmitted to the requestor when the node receives a subsequent token

granting it access to transmit.

Nodes can also transact messages containing local and remote operating statistics.

These include information such as identification of active nodes, current software

version, network activity, and error reporting. If a node transmits a request to read

statistics in another node, the entire transaction is completed while the originating

node holds the token.The remote nodeís statistics are imbedded in its

acknowledgement. It is not necessary for the remote node to acquire the token to

transmit the statistics.

After a node sends all of its messages, it passes the token on to the next node.

Protocols for token passing and messaging are transparent to the user application.

Global Database Transactions

When a node passes the token, it can broadcast up to 32 words (16 bits each) of

global information to all other nodes on the network. The information is contained in

the token frame. The process of sending global data when transmitting the token is

controlled independently by the application program in each node.

The global data is accessible to the application programs at the other nodes on the

same network. Each node maintains a table of global data sent by every other node

on the network. Although only one node accepts the token pass, all nodes monitor

the token transmission and read its contents. All nodes receive and store the global

data into the table.

The table contains separate areas of storage for each nodeís global data. Each

nodeís application program can selectively use the global data from specific nodes,

while other applications can ignore the data. Each nodeís application determines

when and how to use the global data.

Global database applications include time synchronization, rapid notification of

alarm conditions, and multicasting of set point values and constants to all devices in

a common process. This allows uniform and rapid transmission of global data

without having to assemble and transmit separate messages to the individual

devices.

Access to a networkís global database is available only to the nodes on that network,

because the token is not passed through bridge devices to other networks. The

userís application can determine which data items are useful to nodes on a remote

network, and forward them as necessary.


30 890 USE 100 00 November 2004

Error Checking and Recovery

Overview When a node sends a data message, it expects an immediate acknowledgment of

receipt by the destination. If none is received, the node will attempt up to two retries

of the message. If the final retry is unsuccessful, the node sets an error which can

be sensed by the application program.

If a node detects a valid transmission from another node using the same address,

the node becomes silent and sets an error which can be sensed by the application.

The node will remain silent as long as the duplicate node continues to participate in

the token rotation. If two devices have been inadvertently assigned the same

address, the application program can detect the duplication and handle it while the

rest of the application continues.

When a node transmits the token, it monitors the network for new activity from its

successor. If the node detects no valid activity, it makes one retry to pass the token.

If no activity is detected after the retry, the node remains silent. This causes the

network to be initialized and a new token sequence to be created.


890 USE 100 00 November 2004 31

Designing for Process Speed

Overview The figure below is an example of a hierarchical approach using bridge plus devices.

The application uses a relatively large count of nodes, but no network contains more

than six nodes.

Token access and message handling can be rapid within the networks that are used

for the control of time-critical processes. For example, the node count on a given

network can be reduced to the minimum that is required for that portion of the

application. Node counts on other less-critical networks can be increased.

Message transactions across the bridges are slower than in single networks,

because the rotation times of the multiple networks are a factor in receiving data

responses from destinations. Because of this, inter-network traffic should be

dedicated to transactions that are less critical for timing, such as data collection and

program downloading.

Hierarchical configuration for improved throughput:

hostUI UI

UI UI UI UI

BP BP

BP BP

BP BP

CPU CPU CPU CPU CPU CPU

CPU CPU CPU CPU CPU CPU

P230 P230

UI = user interfaceBP = bridge plus


32 890 USE 100 00 November 2004

Designing for Deterministic I/O Servicing

Overview The figure below illustrates a designed for deterministic timing of I/O processes. The

I/O network consists only of the CPU and I/O drops. A user interface (UI) device is

connected to a separate network at the NOM port.

Network for deterministic I/O timing

For truly deterministic timing of I/O servicing, reserve the CPUís network for the

nodes used in I/O servicing only. If you require a user interface or other non-I/O

device in your application, connect it to a separate network at a NOM port.

Guidelines for designing networks for servicing I/O processes, with estimates of

network performance, are provided in the Modbus Plus Network I/O Servicing Guide

(840USE10400).

PS CPU NOMI/O

modules

2 2Modbus Plus

3UI

TIOTIOTIO

I/Omodules

DIO

3 4 5 6

Modbus Plus


890 USE 100 00 November 2004 33

Using Peer Cop

Peer Cop Transactions

Point to point data can be transacted while a node holds the token and during its

token pass with Modbus Plus peer cop. Up to 500 words (16 bits each) can be

directed to specific data references in node devices prior to release of the token, and

up to 32 words can be globally broadcast to all nodes as part of the token frame.

Because all nodes monitor the network, each node can extract data that is

specifically addressed to that node. All nodes detect the token pass and can extract

global data messages from the token frame. Defined data references (like controller

discretes or registers) are used as sources and destinations. For example, a block

of registers can be the data source at the transmitting node, and the same block or

another block can be the data destination in the receiving node.

The delivery of peer cop data to destination nodes is independent of the ënext

addressí used in the token pass. The token is always passed to the next node in the

networkís address sequence. The token frame, however, can contain peer cop

global messages that are unrelated to the next address and are globally broadcast

to all nodes.

Each node is configured through its Schneider Electric panel software to handle

peer cop data transactions. Nodes must be specifically configured to send and

receive the data. Nodes that have not been configured for peer cop will ignore the

data transactions.

Sending Data Nodes can be configured to send two kinds of peer cop data:

! global output Up to 32 words of data can be broadcast globally from each

node to all nodes. Source data references are specified in the node configuration.

! specific output Up to 32 words of data can be transmitted to any specific

node. Multiple node destinations can be specified, up to the maximum of 500 data

words. Any nodes on the network can be specifically addressed as destination. A

unique block of references can be specified as the data source for each targeted

node.


34 890 USE 100 00 November 2004

Receiving Data Nodes can be configured to receive two kinds of peer cop data:

! global input Up to 32 words of global data can be received by each node from

each other node on the network. Destination references are specified in the

receiving nodeís configuration. Up to eight blocks of references can be specified,

giving up to eight separate destinations for the data received from each source

node. The incoming data can be indexed to establish the starting point and length

of each block of data to be extracted from the message and delivered to each

destination.

! specific input Up to 32 words of data can be received from any specific node.

Each node on the network can be specifically defined as a data source, up to the

maximum of 500 data words.

The net effect of using peer cop for data transacted is that each sending node can

specify unique references as data sources, and each receiving node can specify the

same or different references as data destinations. When receiving global data, each

node can index to specific locations in the incoming data and extract specific lengths

of data from those points. Data is thus transacted rapidly as part of each token pass

and can be directly mapped between data references in the sending and receiving

nodes.

Applications can be designed in which alarms and setpoints are transmitted

(globally), with required actions by specific nodes also defined (specifically).

Because all nodes detect the token passes, peer cop global data can be rapidly

known to all nodes, with each nodeís specific data requirements also rapidly known

to just that node.

Peer cop data is transmitted as part of the token pass. Therefore, peer cop applies

to each network independently of any other networks that are part of the Modbus

Plus system. Tokens are not exchanged between networks, because they are not

passed through bridge plus devices. Each network maintains its own peer cop

database, with its own system of global broadcasting and specific node addressing.


890 USE 100 00 November 2004 35

A Peer Cop Example

The figure below shows a network with three nodes that are handling peer cop data

transfers. Other nodes are also present elsewhere on the network.

Node 2 currently holds the token and passes it to the next addressed node

(node 3). Nodes 5 and 7 monitor the pass and extract data as they have been

configured to do.

Node 2 transmits two words of specific output for node 5 from its references 10017

... 10048 (32 bits of discrete reference data, a total of two 16-bit words). It also

transmits these same references as specific output for node 7. In the token frame,

node 2 transmits 32 words of global output from its references 40017 ... 40048.

Node 5 has been configured to receive global input from node 2. It places one word

into its reference 30010, and two words (32 discretes) into references 10097 ...

10129. Node 5 indexes into the 32 words of data and maps its 3 words into these

references. Node 5 has also been configured to receive specific input from node 2,

and places it into references 10017 ... 10048.

Node 7 has not been configured to receive global input from node 2, and ignores it.

The node receives specific input and maps it to its references 10201 ... 10216.

Other References

Ignored

Node 5 is also configured to receive specific input from node 10, and node 7 is

configured to receive global input from node 18. These other references are not

involved in the transactions from node 2. Node 5 and 7 could also be configured to

make output transactions when they pass the token.Node 5 and 7 could also be

configured to make output transactions when they pass the token.

Note: The application uses identical references for this data in nodes 2 and 5. The

references could have been different if required.

token pass (to node 3)

40017-40048 (32)

10017-10048 (2)

10017-10048 (2)

global in from 2:

30010 (1)

specific in from 2:

10017-10048 (2)

specific in from 10:

40100-40131 (32)

10097-10129 (2)

global in from 18:

40200-40202 (3)

specific in from 2:

10201-10216 (2)

token monitortoken monitor

node 2 node 7node 5

global out:

specific out to 5:

specific out to 7:


36 890 USE 100 00 November 2004

Expanding the Network

Linear Expansion

The simplest network configuration consists of two or more nodes connected to a

single section.

The figure below shows four nodes connected in a basic dual-cable configuration.

The basic configuration in the above figure will satisfy the network requirements if

all of the following specifications are met:

! no more than 32 nodes are connected to the network cable,

! the total end-to-end length of each network cable is 1500 ft (450 m) or less,

! the difference in length between cables A and B is 500 ft (150 m) or less, between

any pair of nodes,

! the length of each cable segment (between a pair of nodes) is 10 ft (3 m) or more,

and

! the proper type of impedance termination is used at each node site (tapís internal

jumpers removed at inline sites, and installed at end sites).

up to 32 nodes max., 1500 ft (450 m) cable max.500 ft (150 m) cable max. difference, cable A to B

measured between any pair of nodes

cable A

cable B


node 10 node 5 node 64 node 2

programmablecontroller



networkadapter


890 USE 100 00 November 2004 37

Using RR85 Repeaters

If your network requires more than 1500 ft (450 m) of cable, or more than 32 nodes,

you can install RR85 repeaters to expand the network. The repeaters must be sited

so that no single section of the network exceeds the maximum length of 1500 ft (450

m) of cable, and no single section contains more than 32 nodes.

Up to three repeaters can be present in the cable path between any two nodes that

will communicate with each other. As each cable section can be up to 1500 ft (450

m) in length, and you can have up to three repeaters between a pair of nodes, the

maximum length between any pair of nodes in a linear configuration will be 6000 ft

(1800 m).

The figure below shows the maximum linear configuration using RR85 repeaters.

Expanding Dual-

Cable Networks

On dual-cable networks, repeaters must be placed between the same node devices,

maintaining a logical symmetry to the two cable paths. The figure below illustrates

this.

The figure below shows how repeaters are placed on dual-cable networks.

This configuration is proper because the two repeaters are placed between the

same nodes. Placing a repeater on one path, without a repeater at the

corresponding point on the other path, is not a proper configuration.

1 2 3 4

one section 1500 ft (450 m) cable, 32 nodes max.6000 ft (1800 m) cable, 64 nodes max.

sections:

end node end node

RR85repeater

RR85repeater

RR85repeater

Note: The two physical cable lengths can be different, provided the logical

symmetry of the network is maintained.

cable A

cable B

node


RR85repeater

RR85repeater

repeaters are placedbetween the same pairof nodes on each cable

node node node


38 890 USE 100 00 November 2004

Non-Linear Expansion

You can connect RR85 repeaters to create multiple paths, so long as each section

is run along a linear path (no branches to the cable). In effect, you can use RR85

repeaters to create the equivalent of star or tree configurations. This can be useful

where a linear configuration may not be practical due to the layout of your plant

facility.

The figure below shows an example of non-linear network expansion using RR85

repeaters. This is a legal configuration because it satisfies the network

requirements.

! no more than 32 nodes are present on any single section.

! each section is a linear cable path of 1500 ft (450 m) or less.

! no more than three RR85 repeaters are present in the cable path between any

pair of nodes.

The figure below shows a non-linear expansion.

1500 ft cable max.

ND ND ND ND

RR

RR

RR ND ND RR

ND ND

ND ND

ND ND

ND ND

1500 ft cable max.

1500 ftcablemax.

ND = node device

RR = repeater

1500 ft cable max.

1500 ftcablemax.


890 USE 100 00 November 2004 39

Joining Modbus Plus Networks

How the Bridge

Plus Operates

The BP85 Bridge Plus device connects as a node on each of two Modbus Plus

networks. The bridge operates as an independent node on each network, receiving

and passing tokens according to each networkís address sequence. Bridge plus

devices are not applicable to networks used for distributed I/O applications.

The figure below shows three networks (A,B, and C) joined by a pair of bridge plus

devices. The figure shows a single-cable network for simplicity. The bridge plus also

supports dual-cable layouts. One bridge appears on network A at node address 22,

and on network B at node 25. The other bridge is on network B at node 20, and on

network C at node 20.

If a data message intended for a remote node is received at one of the bridgeís ports,

the bridge stores the message and then forwards it to a node address on the next

network as soon as it has received the token to transmit on that network.

Note: Each bridgeís two network addresses are entirely separate and can be set

uniquely for each network.

network A

network B

network C

node node node

BP85bridge plus

node 22

node 25

nodeBP85

bridge plus

node 20

node 20

node

node node node node

node


40 890 USE 100 00 November 2004

Each message frame contains routing information that allows it to be passed

through successive bridges to a final destination node on a remote network. The

routing path is specified when the message is created by the userís application

program. Messages can be routed to a final destination up to four networks away

from the originating node.

The figure below shows an example of the routing path field in a typical message

frame.

The examples in the above figure illustrate routing through three networks. If a

message originates at node 5 on network A and is intended for node address 12 on

network C the message will be forwarded as described below:

! The first routing address contains the bridge address (22) on the originating

nodeís network. The message will be sent to this bridge by the originating station.

! The second routing address contains the bridge address (20) on the next

network. (Note that the first bridge is at node 25 on this network. When node 25

acquires the token, the message will be forwarded from node 25 to node 20)

! The third routing address contains the address of the destination node (12) on the

final network. The rest of the routing path field will contain zeros, indicating that

no further forwarding is needed.

When the first bridge (22) receives the original message, it examines the routing

field and determines that routing is required to its other network port (the next

address in the field is not a zero). The bridge removes its address from the routing

field, shifting the remaining addresses in the field one place to the left and zero -

filling the field from the right. This places the next routing address (20) into position

1 of the field. When the bridge receives the token to transmit on network B, it passes

the message to node address (20) on that network.

The second bridge (20) processes the message in the same manner, removing its

own address from the routing field and shifting the remaining addresses one place

to the left. Node 12 becomes the final destination, as all the remaining contents of

the field are now zeros. When the token is received, the bridge sends the message

to node 12.

Modbus Plusmessage frame

start

routingpath

routing address 1

routing address 2

routing address 3

routing address 4

routing address 5

routing address 1 = 22



routing address 4 and 5 = 0(no further routing)

example:

end


890 USE 100 00 November 2004 41

Using the Bridge Plus

Although adding many nodes to one network is a legal configuration, you might find

that message throughput is unacceptably slow due to the time required for passing

the token. By organizing your application into more compact groups of nodes, you

can improve throughput.

The figure below shows a basic hierarchical approach using bridge plus devices.

With this approach, separate networks contain the devices that must communicate

rapidly in an industrial process. Bridge plus devices join the networks to provide

process information and supervisory control.

The types of devices used in your application determine how many Modbus Plus

networks you can join.

! You can address a programmable controller destination on a remote network,

which is up to four networks away from the originating node (that is, with four

bridges in the message path).

! Host-based network adapters can be addressed up to three networks away

(through three bridges).

! A single Modbus slave device at a bridge multiplexer port can also be addressed

up to three networks away. A slave device that is part of a Modbus network at a

bridge multiplexer port can be addressed up to two networks away (through two

bridges).

node node node node

BP85 BP85bridge plus bridge plus

host andsupervisory node

time-criticalprocess control

time-criticalprocess control


42 890 USE 100 00 November 2004

Bridging Modbus Plus and Serial Devices

How the Bridge

Multiplexer

Operates

The BM85 bridge multiplexer device operates as a standard Modbus Plus node,

receiving and passing tokens in the networkís address sequence. It provides four

serial port connections to allow Modbus Plus nodes to communicate with serial

devices. BM85 models are available for support of Modbus, RS232, and RS485

serial devices.


890 USE 100 00 November 2004 43

Modbus Configurations

Each Modbus port can be configured to support a master device, slave device, or a

network of up to 32 slave devices. Selection of ASCII or RTU mode, baud rate,

parity, stop bits, link timeout value, and function code conversion is also

configurable.

The figure below illustrates four types of Modbus devices connected to a bridge

multiplexer.

Modbus master devices connected to the bridge multiplexer can access any

controller node on the Modbus Plus network, including nodes on remote networks

through bridge plus devices. A master device can also access a slave device

connected to another port on the local bridge multiplexer, or one connected to a

remote bridge multiplexer node on Modbus Plus.

Modbus slave devices can be accessed by a master at the local bridge multiplexer,

or by a master at a remote bridge multiplexer node, or by program functions in your

Modbus Plus application.

Each Modbus port can be configured for the communication mode (ASCII/RTU) and

parameters suitable for its port devices.

For example, in the above figure, the Modbus master devices connected to ports 1

and 2 of the bridge multiplexer can attach to

! any controller on the Modbus Plus network,

! any slave device on the modem network at port 3, or

! the slave controller at port 4.

Application program function blocks in the controllers on Modbus Plus can access

! the slave devices on the modem network at port 3 and

! the controller at port 4.

CPU CPUCPU

BM85bridge

multiplexer1 2 3 4

= Modbus port

J478Modbusmodem

CPU(slave)

P230programming

panel(master)

IBM PCor

compatible(master) Modbus network

1 ... 32 devices

Modbus Plus network (up to 64 nodes)


44 890 USE 100 00 November 2004

Modbus Port Mapping

Each Modbus port has an address mapping table that allows messages and

commands received at the port to be routed as needed. The table converts the

Modbus address in the message to a routing path, allowing it to be routed to a device

on the local Modbus Plus network, to a device on another Modbus Plus network, or

to a device at another Modbus port. The mapping table allows the devices to be

uniquely addressed, even when two or more ports have devices using the same

Modbus address.

For example, in the figure below, both ports 1 and 3 have networks of Modbus slave

devices. Devices on the two networks can have the same addresses. Commands or

messages originated at the controllers on Modbus Plus can be routed to a unique

device on either of the two Modbus networks. Similarly, the Modbus master device

at port 2 can attach to a unique device on either network.

If a Modbus Plus networked controller or Modbus master device needs to perform a

lengthy command sequence to one of the Modbus networked devices, the bridge

multiplexer can acknowledge the command and then handle it locally at the Modbus

port. The bridge multiplexer will perform a polling process with the destination device

and return a final response when the command action has been completed. This

frees the network at the port for further transactions with other devices in the

application.

CPU CPUCPU

BM85bridge

multiplexer1 2 3 4

= Modbus port

J478Modbusmodem

CPU(slave)

IBM PCor

compatible(master) Modbus network


ASCII, 9600 baud

RTU, 9600 baudRTU, 4800 baud RTU, 4800 baud

J478Modbusmodem

addresses 1 ... 247Modbus network

addresses 1 ... 247


890 USE 100 00 November 2004 45

RS232 and RS485

Configurations

You may program two BM85 models to support custom RS232 or RS485

applications. Both models may be downloaded with a user application image across

Modbus Plus.

The downloaded image contains all of the internal operating code to be used in the

BM85. It provided the protocols for the serial devices to establish communication

with other devices: handshaking, protocol translation, packaging of messages,

buffer space, data conversion, and error handling.

The image can contain all of the serial port parameters (for example, baud rates and

parity) as fixed parameters. The image could also provide a local protocol (default

parameters and a menuing system) for the user to locally configure the parameters

through a terminal at one of the serial ports.

The BM85 can operate as a fully-programmed Modbus Plus coprocessor in the user

application. It can locally manage processes at its serial ports, initiating or

responding to Modbus Plus nodes as needed for higher-level status reporting and

control. Library functions are provided for creating multiple tasks within the BM85ís

application program, and for assigning and arbitrating the tasks.

The BM85 application development tools include:

! a Borland C/C++ run - time startup routine

! an object library of BM85 utility routines, including functions for managing multiple

tasks within the BM85 application

! a Modbus Plus data transfer utility routine

! a header file containing function prototypes

! a compiled demonstration program, with source code, showing examples of the

use of functions in a typical application

! test utilities, including source code, that exercise BM85 hardware

! the download utility for loading the application to the BM85

The software development tools are supplied on both 3.5-inch and 5.25-inch high-

density diskettes.

Step Action Comment

1 Create the application program on an

IBM PC/AT-compatible, using software

development tools supplied with the

BM85.

These require the use of a Borland C/C++

development environment which you

must supply.

2 Download the application using a utility

supplied with the development tools.

The downloaded host can be connected

to Modbus Plus by a Schneider Electric

SA85 (ISA/AT bus) or SM85

(MicroChannel bus) network adapter.


46 890 USE 100 00 November 2004

The figure below summarizes the layout of port devices in a typical BM85 user-

programmed application. As shown, a Modbus master or slave device could also be

attached at a serial port if the user-defined code in the BM85 included a Modbus

protocol handler.

CPU CPUCPU

BP85bridge

multiplexer1 2 3 4

= Modbus Plus

barcodereader

display


scale

Modbusdevice

890 USE 100 00 November 2004 47

2Elements of Network Planning

At a Glance

Overview This chapter discusses the elements of network planning.



Topic Page

An Overview of Network Planning 48

Defining the Network Components 50

Defining the Network Layout 52

Elements of Network Planning

48 890 USE 100 00 November 2004

An Overview of Network Planning

Overview You should consider the following factors in the layout of your Modbus Plus network

planning.

! You can design your control system from a wide range of controller performance

features. You can choose your system layout from many variations in distributed

control, local, and remote input/output systems, and user interfaces. A major

factor determining your Modbus Plus networking requirement will be your

definition of the types, quantities, and site locations of the programmable control

components required for your application.

! Planning your overall programmable control system is beyond the scope of this

document. For further information refer to related publications (see p. 10).

! If you intend your network to primarily service I/O processes, refer to Modbus

Plus Network I/O Servicing Guide (840USE10400) for further guidelines and

performance estimates for these kinds of applications.

! Typically, you define the site locations of your system components according to

your process flow and work cell layout. Your network design should support your

requirements for the transfer of information between those processes. Your

design should also accommodate any host or supervisory computer involved in

the job of monitoring the process activity, loading configuration and recipe files,

retrieving statistics, and providing reports.

! Your network layout should provide ready access for debugging your application

and for future maintenance. Plan to include extra inline taps and drop cables at

convenient points. You can use them to connect a device to monitor the network

activity and collect statistics, without having to disconnect an active device. This

service access also allows you to temporarily connect, test, and debug future

devices as you expand your networking application.

Your planning should include preparation of documents that describe the network

plan. These should support ordering of materials, installation of the network, and

future maintenance. Worksheet examples are provided in this guidebook. Youíll also

find blank worksheets. You can make photocopies of them to document your

network.


890 USE 100 00 November 2004 49

Preparing a Network Plan

This chapter provides a focus for planning your Modbus Plus network requirements

and layout. Planning elements include:

! defining the network media components network trunk cable, taps, and

drop cables

! defining the network layout defining environmental requirements, estimating

cable run and cut lengths, and providing access for future maintenance

! defining the network device setup parameters Certain kinds of devices

require a network node address and other parameters to be set in hardware

switches or in a software configuration. Your planning should include defining the

specific setup parameters for each networked device.

Network devices requiring the specification of setup parameters include:

! programmable controllers Define each controllerís network node address. If

you use its Modbus to Modbus Plus bridge mode, you must set port parameters

for its Modbus port. Setup information is supplied with each controller.

! network option modules Define each network option moduleís node address

and its slot position in the backplane.

! DIO drop adapters and TIO modules Define the node address for each of

these devices in your application.

! host-based network adapters Define the network adapter boardís network

node address and memory window address. You also must edit your host

computerís CONFIG.SYS file. Setup information is supplied with each adapter.

! bridge multiplexers Define each bridge multiplexerís network node address.

You must also define the communication parameters for each serial port that will

be used in your application. Setup information is supplied with each adapter.

! repeaters No special setup information is required for repeaters. This user

manual provides installation information.

! bridge plus Define a network node address for each of the bridge plus

deviceís two network ports. This user manual provides setup and installation

information.


50 890 USE 100 00 November 2004

Defining the Network Components

Overview The figure below summarizes the components of the network cable system.

For ordering information, visit http://www.schneider-electric.com for your nearest

Schneider Electric affiliate.

Modbus Plus

Trunk Cable

Cable specified for Modbus Plus trunk use is available from Schneider Electric with

the following part numbers.

Your cable runs directly between the network device locations. Each cable segment

must be a continuous run between the taps at two locations. Do not use splices,

splitters, or any other configurations, such as star or tree configurations. The only

allowed media components are the network cable and taps.

You typically plan your cable runs according to the horizontal distances between

sites. When you order trunk cable, order it by reels of fixed length. Order reels

sufficient length to allow continuous runs between the network devices.

end

taptrunk cable

drop cable

node

ground connectionthrough drop cable

= internal jumpers connected = internal jumpers disconnected

inlinenode

endnode

inlinenode

Length of Cable on Real Part Number

100 ft (30.5 m) 490NAA27101

500 ft (152.5 m) 490NAA27102

1000 ft (305 m) 490NAA27103

1500 ft (457 m) 490NAA27104

5000 ft (1525 m) 490NAA27106


890 USE 100 00 November 2004 51

Modbus Plus Drop Cables

A drop cable is used at each site to connect between the tap and a network node

device. The cable is preassembled with a 9-pin D connector on one end for

connection to the node device. The other end is open for connection to the tap.

Cables are available in two lengths with the following Schneider Electric part

numbers:

Order a sufficient quantity of drop cables and taps to allow extra ones for service

access and spares.

Modbus Plus Tap A tap is required at each site on the trunk cable to provide connections for the trunk

cable and drop cable. Its Schneider Electric number is 990NAD23000.

Order a sufficient quantity of taps and drop cables to allow extra ones for service

access and spares.

Modbus Plus Cable Impedance

Termination

Each tap contains an internal terminating resistor that can be connected by two

jumpers. Two jumper wires are included in the tap package but are not installed. At

the taps at the two ends of a cable section, connect both of the jumpers to provide

the proper terminating impedance for the network. Taps at inline sites must have

both jumpers removed. See Introducing the Modbus Plus Network (see p. 11) for the

definitions of cable sections and end and inline sites.

The impedance is maintained regardless of whether a node device is connected to

the drop cable. Any connector can be disconnected from its device without affecting

the network impedance.

Modbus Plus

Network Grounding

Each tap has a grounding screw for connection to the site panel ground. Schneider

Electric drop cables have a grounding lug in the cable package. This must be

installed on the cable and connected to the grounding screw on the tap.

The node device end of the drop cable has a lug which must be connected to the

node deviceís panel ground. The network cable must be grounded through this

connection at each node site, even when the node device is not present. The ground

point must not be left open. No other grounding method can be used.

For a full description of Schneider Electric controller system grounding

requirements, refer to related publications (see p. 10).

Length of Cable Part Number

8 ft (2.4 m) 990NAD21110

20 ft (6 m) 990NAD21130


52 890 USE 100 00 November 2004

Defining the Network Layout

Component

Locations

The maximum cable length allowed for the network section from end to end is 1500

ft (450 m). Up to 32 nodes can be connected within this length. The maximum length

includes the total set of cable runs, including all horizontal runs and vertical cable

drops to the networked devices. On dual-cable networks, the difference in length

between cables A and B must not exceed 500 ft (150 m) between any two nodes on

the same cable section. This is explained in more detail on the next page.

The minimum length allowed between any two points is 10 ft (3 m). If two devices

are closer than this, you must include extra cable to attain the minimum cable length.

Environmental

Requirements

Select a cable routing method that will protect the cable from physical damage and

potential electrical interference sources.

Avoid areas of high temperatures, moisture, vibration, or other mechanical stress.

Secure the cable where necessary to prevent its weight and the weight of other

cables from pulling or twisting the cable. Plan the cable layout to use cable ducts,

raceways, or other structures for protecting the cable. These structures should be

dedicated for signal wiring paths, and should not contain power wiring.

Avoid sources of electrical interference that can induce noise into the cable. Use the

maximum practicable separation from such sources.

Follow these cable routing guidelines for electrical protection:

! Maintain a minimum separation of 3.3 ft (1 m) from the following equipment: air

conditioners, elevators, escalators, large blowers, radios, televisions, intercom

and security systems, fluorescent, incandescent, and neon lighting fixtures.

! Maintain a minimum separation of 10 ft (3 m) from the following equipment: power

wiring, transformers, generators, and alternators.

! In addition to the minimum separation, if the cable must cross power wiring

carrying over 480 volts, it must cross only at a right angle. The cable must not run

parallel to the power wiring.


890 USE 100 00 November 2004 53

Adding Service Connectors

In addition to the drop cables to the network node devices required for your

application, you should provide one or more drops to allow for service access to the

active network.

Include at least one drop at a location that will allow connection of a device for future

monitoring and servicing, without disconnecting some active device. This can also

assist in debugging your application at the present time and for future expansion.

Dual-Cable

Length

Considerations

Designing your network as a dual-cable layout can give you increased protection

against communication errors caused by cable breakage or excessive electrical

interference. If a fault occurs on either cable path, the node devices can continue

processing error-free messages on the alternate path.

To minimize the chance of simultaneous interference or damage to both cables,

route the two cables through separate areas of your plant site. Typically, this

requires you to plan different lengths for the two cable paths between successive

nodes. Additional considerations apply when the two cable lengths will not be the

same.

Between any two nodes on the same cable section, the difference between the

lengths of cables A and B must not exceed 500 ft (150 m). Figure 26 shows an

example of an illegal configuration. Even though the two cable lengths between

nodes 1 ... 4 are identical at 1200 ft (360 m), several illegal lengths exist in this

configuration.

! Between nodes 1 and 2, the difference in lengths between cables A and B is 600

ft (180 m). This exceeds the maximum allowable difference of 500 ft (150 m).

! Between nodes 2 ... 4, the difference between cables A and B is also 600 ft (180

m). This exceeds the maximum allowable difference of 500 ft (150 m).

NETWORK PERFORMANCE

Before you connect or disconnect any devices on an active network, you should be

aware of its affect on network timing. See network performance (see p. 55) for

further information about predicting network throughput and node dropout latency

time.

Failure to follow this precaution can result in injury or equipment damage.

CAUTION


54 890 USE 100 00 November 2004

The cable A to B difference only applies to node connections on the same cable

section. If node 4 were a repeater or bridge plus, for example, the cables on the

other side of that node would be totally independent of the cables in the above

figure, for measurement purposes.

Estimating Cable

Run Distances

Your layout planning should provide information to the installers that will show the

cut length of each segment in the cable run. Before the cable is cut at each drop

location, the following factors should be considered:

! The cable routing must provide for installation of strain relief to prevent the

cableís weight from pulling on its connector at the node device. The cable should

be routed adjacent to a frame, panel, or other stable structure to properly secure

strain reliefs against its weight. Allow sufficient cable length for this routing.

! Provide a service loop at each node device to allow future servicing of the device

without placing stress on the cable or connector. A service loop of 6 in (15 cm)

minimum radius is adequate for most panel mounting layouts.


not to scale 900 ft(270 m)

150 ft(45 m)

150 ft(45 m)

300 ft(90 m)

450 ft(135 m)

450 ft(135 m)

890 USE 100 00 November 2004 55

3Estimating Network Performance

At a Glance

Overview This chapter discusses network performance.

Estimating Network Performance

56 890 USE 100 00 November 2004



Topic Page

Estimating Network Performance 57

Factors for Planning 59

How Devices Interact on the Network 60

Factors That Affect Performance 61

Communication Paths and Queuing 63

Reading and Writing with the MSTR 65

A Sample MSTR Communication 67

Getting and Clearing Statistics 69

Reading and Writing Global Data 71

Loading Effects in Your Application 72

Predicting Token Rotation Time 74

Formula for Calculating Rotation 75

Predicting MSTR Response Time 76

Estimating Throughput (With MSTR) 78

Estimating Throughput (With Peer Cop) 80

Predicting Node Dropout Latency Time 82

Estimating Latency for a Small Network 84

Estimating Latency for a Large Network 86

Planning for Ring Join Time 88

Precautions for Hot Standby Layouts 90

Guidelines for a Single Network 91

Guidelines for Multiple Networks 95

Sample Communications Across Networks 98

A Summary of Network Planning 100


890 USE 100 00 November 2004 57


Overview This chapter describes the major factors you should consider as you plan the layout

of your Modbus Plus network. It explains how you can use MSTR and peer cop

methods for communicating in your application, and shows how your use of these

methods affects network performance. It gives examples of message handling

between nodes, and presents guidelines for predicting the performance of single

and multiple networks.

Your Network

Performance Goal and Options

The goal of your planning guide is to achieve a network design that meets your

needs for information transfer among the devices in your application. The networkís

message handling capacity must be sufficient to assure that each device has the

data it needs, within the timing requirements of your application and with margins for

safety. The network design must also be able to support future modifications and

expansion to your application.

Each device presents unique requirements for obtaining data from the other

devices. Data requirements can range from occasional updates of statistics to nearly

continuous exchanges of large blocks of information. Control applications that

interact between nodes require a network design that provides fast responses to

request for data.

When multiple devices share the same network, each deviceís data requirements

should not be viewed as being isolated from the requirements of the other devices.

Each device has a need for access to the network token. The length of time each

device needs to transmit its application messages affects the networkís token

rotation time, and therefore also affects the networkís access for the other devices.

Response to data requests are also determined by the processing speeds of the

devices, such as the scantimes of programmable controllers and the efficiency with

which their application programs have been designed. The network should be

viewed as an interactive array of devices, in which overall performance is affected

by the physical count of nodes, their combined data requirements, and their data

handling capabilities.


58 890 USE 100 00 November 2004

Your Option You can plan your network application as a single network, with a linear

arrangement of nodes. You can also plan it as multiple networks that are joined in a

layered or hierarchical configuration. The choices you make will be determined by

your data requirements between the nodes. Nodes which much exchange

significant amounts of data that is critical to the timing of some process should be

positioned on a compact network, with a bridge serving to forward less - critical data

to devices on other networks.

Consider also how much of the data should be handled through read/write message

transactions between the nodes, and how much through global database

transactions. If your application requires that devices must maintain multiple

concurrent transactions with other devices, consider how many data paths can be

opened within the devices.

As you choose your design options, your estimation of total throughput for your

network application should be conservative. When you estimate ëaverageí

performance, be aware that events in your application will occur asynchronously,

and will place heavier loads on the network at various times. Instantaneous

throughput between devices in a time - critical process must remain within safety

margins, even with worst case loading.

By understanding the factors that affect your networkís performance, and your

option for device selection and programming, you can achieve a network design that

meets the goals for your current application and future needs.

Design Options

for I/O Servicing

If you are designing your network primarily for servicing I/O field devices through

DIO drop qdapters and TIO modules, you will have several important factors to

consider.

Your network must service the I/O processes at a rate of speed that is sufficient to

control them efficiently and without excessive delay. In general, the networkís I/O

servicing rate will depend upon the amount of nodes you employ, and the average

message size. In addition, the determinism or repeatability of the I/O servicing rate

will be affected by the types of node devices you connect to the network.

To assist you in planning for both of these factors (the speed of timing for data

transfers, and the repeatability of that timing), a guidebook is available for network

applications that are intended for I/O servicing. Seed the Modbus Plus Network I/O

Servicing Guide (840USE10400) for further details.


890 USE 100 00 November 2004 59

Factors for Planning

Overview When you plan communications strategy that will integrate various control systems

and computer products, consider the kinds of applications you will implement, their

information requirements, and their control devices. Your planning should include

three levels.

! network applications

! information requirements

! transaction requirements

Network Applications

Consider the following types of applications for your network.

! process data acquisition

! supervisory control

! user interface

! statistical process control

! statistical quality control

! local and remote programming

! program archiving, upload, and download

! database generation for management reports

! connectivity to other types of networks

Information

Requirements

Consider the following information, which is involved in all applications and between

applications.

! process data between interactive nodes

! downloading recipes and control programs

! production/quality statistics and reports

! supervisory control and information for user interfaces

! data conversion to computer databases

! process device diagnostics and maintenance reports

Consider the quantities of each type of information and their throughput

requirements. Note how much data must be transferred between devices per unit of

time.

Transaction Requirements

Consider the types and quantities of message transaction that must occur between

networked devices. Make a chart showing your planning for each transaction

Originating Node network number

node address

device description

device type

Receiving Node network number

node address

device description

device type

Communication purpose

priority

sent under what conditions

frequency of enabling

numbers of registers

response time needed


60 890 USE 100 00 November 2004

How Devices Interact on the Network

Overview Multiple data transfer and programming operations can occur concurrently on a

network. The network example below shows five nodes on a single network. In

practice, the network could contain up to its full complement of 64 nodes, and

additional networks could be connected through bridge plus devices.

Control processes can be in progress between various nodes while plant personnel

are actively programming, archiving, and diagnosing the devices from different

locations.

Examples of operations which can be occurring concurrently on this network

include:

! data transfers in progress between controllers 2 and 4

! computer A operating as a user interface obtaining data from controllers 2 and 4

! computer B in a programming or load/record/verify operation with controller 3

! plant personnel accessing any nodes from the P230 programming panels using

the controllersí built-in Modbus to Modbus Plus bridge mode

controller controller controller controller

Modbus Plus Network


node 3

P230

programming

panel

P230

programming

panel

controller


890 USE 100 00 November 2004 61

Factors That Affect Performance

Handling

Multiple

Operations

The time that is required for a node to respond to a request for data is affected by

the count of nodes on the network, by the number of active transactions in each

node, and by each nodeís instruction handling capability (scan time). The way in

which you program your application also will affect the response time.

Consider the multiple operations example again. Data transfers are in progress from

controllers 2 and 4. Computer A is operating as a user interface obtaining data from

controllers 2 and 4. These two operations can be considered to be the most critical

for timing, because they are handling application data in real time. These operations

are also interactive because the application uses computer A as an interface

accessing data in the controller 2 and 4. Data paths and application program

instructions must be provided in these controllers for servicing the user interface, in

addition to servicing their mutual data requirements.

Two additional operations are occurring on the network. Computer B is in a

programming or load/record/verify operation with controller 3. Plant personnel

accessing any node from the P230 programming panels using the controllersí built-

in Modbus to Modbus Plus bridge mode. These operations are handling data that is

not currently used in the application. Their activity on the network will, however,

affect the response time for the first two operations. For example, the networkís

token must be held for a period of time by computer B and controller 3 while they

transact the necessary data. If this operation terminates, and these nodes have no

other immediate operations, each will retain the token for only a minimum time

before passing it. (Methods for estimating token rotation time are presented later in

this chapter.)

controller computer A controller

Modbus Plus Network


node 4

P230

programming

panel

P230

programming

panel

controller

computer B


62 890 USE 100 00 November 2004

Planning Your Application

Program

The way in which you program your application will also affect network performance.

For example, the approximate time required between two controllers to request data

and receive it is:

! one token rotation time for network access to send the request

! one scan time in the receiving controller to process the request

! one token rotation time for network access to send the response

! two scan times in the initiating controller to process the response

If data is transferred as a global transaction, it is received by multiple nodes during

a single token pass. The approximate time for this is:

! one token rotation time for network access to send the global data

! one scan time in each receiving controller to process the global data

Your choice of polling or unsolicited transactions will greatly affect network

performance. If you construct your application program using polling techniques,

you will force the network to handle some quantity of transactions that do not return

data. This will tend to increase the aggregate amount of network traffic and will

diminish the ability of the network devices to manage their data paths and to acquire

the token.

Rather than using polling techniques, you can gain improved message throughput

by implementing event-driven read or write operations between the devices.

Receiving devices can be prepared for unsolicited data by having their application

sample flag bits (bits that are written by the incoming data, and cleared by a

subsequent scan), or by using transaction counters or other similar methods.


890 USE 100 00 November 2004 63

Communication Paths and Queuing

Overview With multiple devices processing messages asynchronously on the network, it

becomes possible for an individual device to have several concurrent transactions

in process. The peer processor in each device maintains multiple communication

paths of various types. It opens a path then a transaction begins, keeps it open

during the transaction, and closes it when the transaction terminates. When the path

is closed, it becomes available to another transaction.

Both the originating and destination devices open paths and maintain them until the

transaction completes. If the transaction passes through bridge plus devices to

access a destination on another network, each bridge opens and maintains a path

at each of its two network ports. Thus a logical path is maintained between the

originating and destination devices until the transaction is finished.

Path Types Each Modbus Plus device has the following types of paths:

! data master path for data reads and writes and for get and clear remote statistics,

originated in the device

! data slave path for data reads and writes as they are received in the device

! program master path for programming commands originated in the device

! program slave path for programming commands as they are received in the

device

Each path is independent of the others. Activity in one path does not affect the

performance of the other paths.

Path Quantities The following paths are available in the various types of Modbus Plus devices:

Data Master

Paths in Controllers

Five data master paths are provided in controllers. Of these, one path is reserved

for use by the controllerís Modbus port in the bridge mode between Modbus and

Modbus Plus. The remaining four paths are reserved for use by MSTR functions in

the controllerís application program.

CPU BM85 BP85 SAB5/SM85

Data Master 5 4 8 8

Data Slave 4 4 8 8

Program Master 1 4 8 8

Program Slave 1 4 8 8


64 890 USE 100 00 November 2004

Queuing If all data slave paths are active in a device, incoming transactions will be queued.

Transactions will remain queued until a path is available, and will then be removed

from the queue and given the path. A final data response is not returned to your

application until a full path is available from origin to destination.

When the destination node removes a transaction from its queue, it must acquire the

token and request the command again from the originating node. The originator will

respond with the command again from the originating mode. The originator will

respond with the command while the destination has the token. This process occurs

automatically, eliminating the need for polling between the origination and

destination in your application.

BP85 Bridge Plus

Queuing

Messages which must pass through multiple bridges will be queued (if necessary)

within the first bridge, but will not be queued within any subsequent bridges in the

transaction path. The figure below shows an example of a BP85 Bridge Plus

queuing.

A message from controller A to controller B must pass through two bridge plus

devices. If a path is not available in the first bridge, the message will be queued and

given a path when one is available. If the second bridge does not have a path when

it receives the message, the message will not be queued further. An error code will

be returned from the second bridge and can be sensed by the application program

in controller A.

Transactions are handled in this way to prevent excessive delays between requests

and responses in your application. This situation should occur rarely, and is caused

by high message loading within the bridge.

Modbus Plus network

Modbus Plus network

controller A

peer processor

peer processor

Modbus Plus network

bridge plus

destination

peer processor

peer processor

bridge plus

peer processor

controller B

peer processor

origination


890 USE 100 00 November 2004 65

Reading and Writing with the MSTR

Overview The MSTR instruction is a ladder logic function that provides access to the Modbus

Plus network. Its format is shown in the figure below.

A complete description of how you can program your application using the MSTR is

provided in the Ladder Logic Block Library User Guide (840USE10100), which will

help you follow the sample communication on the next page.

The control block is a 4x reference that is the starting register in a block of nine

consecutive registers. These registers define the intended actions and Modbus Plus

routing for the communication. Their contents are unique for each type of operation.

For example, in a data read or write operation, the control block layout is as follows:

The control block register at 4x + 2 specifies the length of the data area for the read

or write operation. For example, if this register contains a value of 32 decimal, that

many registers of data will be transferred in the operation.

Register Content

4x Operation Type 1 = White

2 = Red

4x + 1 Storage for Returned Error status Code

x + 2 Data Block Length 4

4x + 3 Start with the data area in the Destination Device

4x + 4 Modbus Plus Routing Path 1





control block

(4XXXX)

data area start

(4XXXX)

MSTR

data area size

(N)

enable

abort

active

error

complete

summary of MSTR operations

write

read

get local statistics

clear local statistics

write global database

read global database

get remote statistics

clear remote statistics

peer cop health

1

2

3

4

5

6

7

8

9


66 890 USE 100 00 November 2004

The control block register at 4x + 3 defines the starting location of the data buffer in

the destination device. Its contents are an offset value (not an absolute address).

For example, a value of 1 specifies reference 40001 in a programmable controller.

The offset can be incremented in successive MSTR operations to move large areas

of data.

Data area start is a 4x reference that is the starting register in a block of up to 100

consecutive registers that will be used at the local data buffer in the read or write. If

the operation is a read, the incoming data from the destination device will be stored

into this buffer. For a write, the buffer contents will be sent to the destination device.

Data area size is an absolute value in the range 1 ... 100 decimal. It specifies the

maximum quantity of registers to be allocated for the MSTR functionís data area.


890 USE 100 00 November 2004 67

A Sample MSTR Communication

Overview Every Modbus Plus device has a peer processor that controls network

communication. Collectively the peer processors in all of the networked device

establish and maintain the token rotation, the transmission and receipt of messages,

and acknowledgements. In a programmable controller, the peer processor transfers

message data to and from the MSTR functions in your ladder logic.

The figure below shows two controllers on a Modbus Plus network. Here is an

estimate of the time required for a read operation.

During the ladder logic scan in unit A, an MSTR block is executed that specifies a

read request to unit B. At the end of the block execution, the read request is sent to

the peer processor in unit A. The following events occur.

Step Action Result

1 When the peer processor in unit A

acquires the network token, it transmits

the read request.

When the request is received by the

peer processor in unit B, it sends an

immediate acknowledgement.

2 At the end of the ladder logic scan in unit

B, the incoming transactions are handled.

The peer processor in unit B is ready

with the data response to the read

request.

3 When the peer processor in unit B

acquires the token, it sends the data

response to unit A.

The peer processor in unit A sends

immediate acknowledgement.

4 At the end of the logic scan in unit A, the

incoming transactions are handled. The

transaction is complete at the next solve

time of the MSTR function in unit A.

Data registers will be written, and the

MSTR functionís complete output

goes on.

Modbus Plus network

controller A

peer processor

controller B

peer processor

request

response


68 890 USE 100 00 November 2004

The time required to process the complete communication would be:

If the scan time in unit B is much shorter than the token rotation time, unit B can

create the data response and have it ready before the token reaches unit Bís peer

processor. On the other hand, if a data slave path is not free in unit B, the request

will be queued by that unitís peer processor and will wait until a data slave is free.

Refer to transaction timing elements (see p. 162) for more information about the

frame format of Modbus Plus messages.

Event Time Range Average Time Worst Case Time

1 0 ... 1 token rotation 1/2 token rotation 1 token rotation

2 0 ... 1 scan, unit B 1/2 scan, unit B 1 scan, unit B

3 0 ... 1 token rotation 1/2 token rotation 1 token rotation

4 0 ... 2 scans, unit A 1 scan, unit A 2 scans, unit A


890 USE 100 00 November 2004 69

Getting and Clearing Statistics

Local Device Statistics

When you issue commands to get local statistics or clear local statistics, the action

is handled by the local deviceís peer processor. No transaction occurs on the

Modbus Plus network. The operation is completed by the end of the MSTR function

execution in the local device.

The figure below illustrates a get local statistics operation in controller A.

Modbus Plus network

controller

peer processorresponse request

not used in transaction


70 890 USE 100 00 November 2004

Remote Device Statistics

When you issue commands to get remote statistics or clear remote statistics, the

action is handled by the destination deviceís peer processor. Timing of the

transaction is affected by the network token rotation time and the scan time of the

originating device. The scan time of the destination device is not a factor.


Time Range Average Time Worst Case Time

0... 1 token rotation 1/2 token rotation 1 token rotation

0... 2 scans, unit A 1 scan, unit A 2 scans, unit A

Modbus Plus network

controller A

peer processor

controller B

peer processor

request

response


890 USE 100 00 November 2004 71

Reading and Writing Global Data

Passing Global Data Between

Nodes

Up to 32 registers of global data can be included in the network token frame as it is

passed between nodes. In the node currently holding the token, as MSTR function

can be programmed to include global data in the next token pass. The global data

will be read into the peer processors of the other nodes on the same network, and

will update the storage area in those nodes. Global data is not passed through

bridges from one network to the next.

The application program in each node can have an MSTR programmed to read all

or a certain portion of the global data. Nodes accept global data without waiting for

paths or queuing.

The figure below shows a sample global database pass.

During the ladder logic scan in unit A, an MSTR block is enabled that specifies a

write global database operation. At the end of the block execution, the global data is

sent to the peer processor in unit A. The following events occur:


Step Action Result

1 When the peer processor in unit A acquires the

network token, it transmits any other

application message in has pending, and then

passes the token.

Every other node on the network

reads the global data contained in

the token frame and places a copy

of it in its peer processor.

2 Each other controller on the same network, an

MSTR function programmed to Read Global

Database can read the new global data.


1 0... 1 token rotation 1/2 token rotation 1 token rotation

2 0... 1 scan, unit B... n 1/2 scan, unit B 1 scan, unit B

Modbus Plus network

controller A

peer processor

token pass

controller B... N

peer processor

All other nodes on thisnetwork can access datain the token frame.


72 890 USE 100 00 November 2004

Loading Effects in Your Application

Nodes During the application, each node on the network can have a different number of

paths constantly being opened, held active, and closing. This is a dynamic process

that is affected by the count of nodes and the amount of message traffic between

them.

If some nodes have most of their paths active at any given moment, and others do

not, the nodes with the heavy path loading will hold the token longer as the process

data. The token will move more slowly through those that are lightly loaded.

The effect on an individual MSTR function in your application will be quicker

completion during light network loading, and slower completion under heavier loads.

Even though the origination and destination nodes in the MSTR operation may have

light path loading, the network token must still pass through the other nodes. If their

loading is heavy, the net effect will be a slower token rotation time, affecting both the

sending and response of a data request.

Refer to transaction timing elements (see p. 162) for further information about the

token holding times in nodes that are fully loaded with active transactions and

queuing.

MSTR Data Path

Handling Under

Loading

When you program multiple MSTR functions in a controllerís ladder logic, they will

be handled according to loading conditions as follows:

! at the source If more than four MSTR functions are enabled at any time

(through their ENABLE inputs), the first four scanned will go active using the

MSTR Data Master paths available in the controller. The other MSTR functions

will not be serviced, but will wait for free paths. Your design of the ladder logic

program controls the sequencing of the MSTR functions.

! at the destination If the destination controller has all of its data slave paths

currently active, the next data transactions will be queued until paths are

available. This queue will be processed at the approximate rate of four

transactions per scan of the controller. MSTR functions in originating controllers

will wait, with their paths held open, until a final data response is returned from

the destination.

During dequeuing at the destination, the receiving node will request the command

again from the originating node when the receiving node acquires the network token.

The command is reissued and received while the receiving node holds the token.

This process eliminates the need for continual polling, reducing the overhead in your

application and the loading that would be caused by polling on the network. It does,

however, tend to add some loading and to decrease the overall message

throughput. By adopting techniques to minimize queuing, such as logically grouping

the nodes on each network, using global data transactions, and packing more data

into fewer MSTR transactions, you can achieve fast response times and high data

rates in your process.


890 USE 100 00 November 2004 73

Modbus Port Data Path

Handling Under

Loading

The dedicated data master path for a controllerís Modbus port in bridge mode is

always available. Transactions are given to the peer processor as received from the

master device connected to the port, and are transmitted when the token is

acquired.

Data slave paths in the receiving device will be queued as necessary if multiple

messages are initiated to the same device.

Program Path

Handling Under

Loading

Program master and program slave paths are not queued. Only one programmer

can have access to a controller at any given time. An attempt to attach a second

programmer will return an error message to that device.


74 890 USE 100 00 November 2004

Predicting Token Rotation Time

Overview The figure below shows a graph of token timing as a function of the network node

count and message loading. The graph was constructed with a network containing

Schneider Electric programmable controllers. Message loading ranges from zero

(the token pass only) to maximum loading. (Each controller has all four MSTR data

master paths on, with each path passing 100 registers and global data passing 32

registers.)

A token only

B 32 register global data

C 32 register global data and 1 data master path always on (100 registers)

D 32 register global data and 2 data master path always on (200 registers)

E 32 register global data and 3 data master path always on (300 registers)

F 32 register global data and 4 data master path always on (400 registers)

The token rotation times shown in the figure are for data transactions, with no

queuing at the destination nodes and no remote programming concurrently in

progress. Rotation times can be longer if some nodes must hold the token for a

longer time to process queued transactions or remote programming.

Token rotation time will be slightly reduced when less than 100 registers of data are

moved in each path; however, this improvement will be marginal for most

applications. Optimum throughput can be expected by using relatively few data

master paths (and enabled MSTR functions) at a time, with each path moving as

much data as possible.

500

400

300

200

100

5 10 15 20 25 30

time (ms.)

nodes

A

F

E

D

C

B


890 USE 100 00 November 2004 75

Formula for Calculating Rotation

Overview The formula for calculating the average token rotation time is

TR = (2.08 + 0.016 * DMW) * DMP + (0.19 + 0.016 * GDW) * GDN + 0.53 * N

where

! TR is the average token rotation time in ms,

! DMW is the average number of words per data master path used in the network

(maximum 100 for controllers),

! DMP is the number of data master paths used continuously in the network (see

the two notes below),

! GDW is the average number of global data words per message used in the

network (maximum 32),

! GDN is the number of nodes with global data transmitted in the network, and

! N is the number of nodes on the network.

For example, consider two cases in which an MSTR is enabled every scan, and the

scan time is 20 ms.

! faster token If the token rotation time is estimated at 10 ms, count the data

master path use as 0.5 path. The ratio (10/20) shows the use in one half path.

! faster scan If the token rotation time is estimated at 50 ms, count the data

master path use as 1.0 path. Even though the ratio (50/20) is greater than unity,

the use will never be more than one path.

Note: When counting data master paths, consider the ration between the networkís

token rotation time and the driverís scan time. The way in which you count paths

depends upon which of these two times is the faster.

Note: First estimate the token rotation time and then refine it after you perform the

calculation. Refer to the chart in Predicting Token Rotation Time (see p. 74) to

make the estimate.

For example, if an MSTR block will be timed to execute every 500 ms and the token

rotation time is estimated as 50 ms, you can estimate the data master path use as

0.1 path (50/500). After you calculate the actual token time from the formula, review

your initial estimate. If the actual time is not close to 50 ms, refine your estimate,

and recalculate the path use.


76 890 USE 100 00 November 2004

Predicting MSTR Response Time

Overview When you have calculated the average token rotation time on the network, you can

predict the average time for a response to an MSTR data request. The response

time will not include factors such as queuing or error conditions on the network. The

time will be based on a request-response transaction on a single network. The

average response time is the sum of the following times.

! 1 token rotation time

! 1 scan time of the requesting unit

! 1/2 scan time of the responding unit

The worst case response time would be

! 2 token rotation times

! 2 scan times of the requesting unit

! 1 scan time of the responding unit

If the scan time of the responding unit is much shorter than the networkís token

rotation time, it is possible for the unit to create the data response and have it ready

in the peer processor before the network token arrives at the unit. In this case the

response would be transmitted when the token is received. The scan time of the

responding unit can be removed from the timing calculation.

The figure below shows an example of a network of six nodes with the planned

loading. In this example, nodes 1 to 4 will transmit using MSTR functions and global

data as shown in the figure. Nodes 5 and 6 will not send data in this application but

will use the global data when they receive it.

Originating Node Types of Communication Receiving Node

1 MSTR always on 50 registers 2

MSTR ON for 500 ms 100 registers 3

MSTR always on 75 registers 4

2 MSTR always ON 100 registers 1

MSTR always ON 75 registers 4

3 Global Data On 16 registers ALL

MSTR always ON 75 registers 4

4 Global Data On 32 registers All

CPU CPUCPU CPU CPUCPU

1 2 3 4 5 6

Modbus Plus network


890 USE 100 00 November 2004 77

Guidelines are provided below for calculating the time required for obtaining data.

The following steps can be used to calculate the data response time for an MSTR

and the acquisition time for global data.

! Find the average token rotation time Section 3.12.

TR = (2.08 + 0.016 * DMW) * DMP + (0.19 + 0.016* GDW) * GDN + 0.53 * N

DMW = (50 + 100 + 75 + 100 + 75 + 75)/6 = 79 words

DMP = (1 + 20/500 + 1 + 1 + 1 + 1) = 5.04 paths

GDW = (16 + 32)/2 = 24 words

GDN = (1 + 1) = 2 nodes

N = 6 nodes

TR = (2.08 + 0.016*79) *5.04 + (0.19 + 0.016 * 24) * 2 + 0.53 * 6 = 21.18 ms

! Calculate the MSTR response time.

If all units have a scan time of 20 ms, then:

! Calculate the global data acquisition

Each unitís time to receive data from another unitís global data write would be

Average Response Time 1 token rotation time

1 scan time of the requesting unit

1/2 scan time of the responding unit

21.18 ms

20 ms

10 ms

Total 51.18 ms

Worst Case Response

Time

2 token rotation times

2 scan time of the requesting unit

1 scan time of the responding unit

42.36 ms

40 ms

20 ms

Total 102.36 ms

Average Time 1/2 token rotation time

1/2 scan time of the receiving unit

10.59 ms

10 ms

Total 20.59 ms

Worst Case

Time

1 token rotation time

1 scan time of the receiving unit

21.18 ms

20 ms

Total 41.18 ms


78 890 USE 100 00 November 2004

Estimating Throughput (With MSTR)

Overview The figure below shows a graph of the throughput per node as a function of the node

count. The data rate is the quantity of registers that can be transferred per second

of time. The graph was constructed with a network containing Schneider Electric

programmable controllers, with each controllerís message loading at maximum.

(Each controller has all four MSTR data master paths on with each path passing 100

registers.)

The throughput shown in the figure below is for data transactions with no global

data, no queuing at destinations, and no remote programming concurrently in

progress.

5 10 15 20 25 30

nodes

432

20Ktotal network throughput = 20k registers/s

15K

10K

5K

registers

throughput/node =20k registers/s

number of nodes

Note: The networkís capacity is 20,000 registers/s. The throughput for any node is

20,000 registers/s divided by the count of nodes on the network.


890 USE 100 00 November 2004 79

Grouping Nodes Logically for

Increased

Throughput

Each nodeís throughput is a factor of the networkís node count and network loading,

as shown in the above figure. Consider how your node devices must communicate

to the other nodes. Plan each network in your application as an integrated system

of devices and application programs that will achieve the required throughput.

Instead of constructing a single network with a large node count, you can realize

improved throughput by integrated smaller, more compact networkís through

bridges.

Compact networks should consist of nodes that need to communicate time-critical

information with one another. Bridges serve to pass any lower-priority information to

devices or remote networks. Using bridges in an application in which all nodes must

communicate time-critical information will not improve throughput. When you plan

your application, consider the communication requirements so that you can

determine the best grouping of nodes. This will also assist you later when you

construct MSTR functions in your application program.

Note: You can include two or more bridges on the same network as a way to pass

data quickly to multiple remote networks. allow margins for instantaneous loading.


80 890 USE 100 00 November 2004

Estimating Throughput (With Peer Cop)

Estimating Total Communication

Time

With peer cop communication, data can be sent to specific nodes during token

passes. Nodes using peer cop can transmit specific output data to one or more

destinations. The destination nodes can be set to receive specific input data from

selected sources.

If the sending and receiving nodes have scan time that are significantly shorter than

the networkís token rotation time, data can sent from a source node, and a response

received back to that node, within a total communication time that is a fraction of the

token rotation time. an example is shown below.

The total communication time between specific output and specific input in a

controller can be estimated using the following formula (times in ms).

one scan time (sending controller) + specific output time (sending controller) +% of

token rotation time (sending node to receive node) + specific input time (receiving

controller) + one scan time (receiving controller) = communication time between

specific output and specific input.

Percent of token rotation time is the portion of the networkís total token rotation time

that elapses between the sending nodeís release of the token and the receiving

nodeís release of the token. The figure below shows a network at the start of a peer

cop transaction between two controllers.

In the figure below, controller A has the token with peer cop specific output traffic for

controller B. Two other nodes exist in the networkís address sequence between

controllers A and B.

The sending node A transmits its specific output data, containing peer cop data to

receiving node B. Node B receives this traffic immediately as specific input data, and

acts upon it during its next scan. The token now passes through the intervening

nodes before it is passed to node B. Node B retains the token while it handles any

ënon peer copí traffic.

Before node B releases the token to the next node in the address sequence, it sends

the peer cop response data (as specific output) for node A, which receives the data

immediately (as specific input) and handles the data during its next scan.

In this communication, the elapsed time for the transaction is the time between the

data transmission from node A (when node B begins to act on its data) and the

transmission from node B (when node A begins to act on its data). Because this

actual time may vary somewhat for subsequent communications between A and B

(due to variable token-holding times in the intervening nodes) it is convenient to

estimate the time as a ëpercent of network token rotation timeí as expressed in the

formula above.

Modbus Plus network

controller A

controller Bnext node next node


890 USE 100 00 November 2004 81

Estimating Specific Input

and Specific

Output Times

Specific input and specific output times for processing data in a node with peer cop

can be estimated using the following formula (times in ms):

specific input/output time =.530 +.001 (words * 16)

For example, if 200 words of data are sent:

specific input/output time =.530 +.001 (200 * 16) = 3.73

Example of Peer Cop

Performance

Consider a network that has an average token rotation time of 100 ms. Two

controllers are involved in the transaction, each with a scan time of 20 ms. The

percent of token rotation time between the two nodes is 30%, for a time of 30 ms.

one scan time, sending controller

+ specific output time, sending controller

+% of token rotation time, sending node to receiving node

+ specific input time, receiving controller

+ one scan time, receiving controller

20.00

3.73

30.00

3.73

20.00

Total 77.46 ms


82 890 USE 100 00 November 2004

Predicting Node Dropout Latency Time

How the Network Handles Node

Dropouts

All active nodes maintain a member node table that identifies other nodes in the ring.

When a node holds the token and completes its message traffic, it passes the token.

The token is always passed to the next active node in an ascending address

sequence. If the next node has left the network since its last token pass, a network

timeout occurs during the attempt to pass the token. The remaining nodes detect

this timeout, and begin to create a new address sequence that will bypass the

missing node.

In the process of creating the new address sequence, all nodes try to reclaim the

token, with the lowest-addressed node invariably claiming and holding it. During this

process, each node builds a new ëmember nodeí list that re-establishes the

sequence. When the ring is re-established the token rotation begins again at the

lowest address. This process is handled automatically by the remaining nodes and

is transparent to the user application, except for the time interval required to

reconstitute the network ring.

The time interval can be calculated separately for each node that remains in the ring.

It represents the time during which the node will not be processing and data

messages. It is called the Node Drop Out Latency time (NDOL), and is expressed in

ms. Nodes can be removed from the network by some fault or by design in the

application, for example for scheduled maintenance on the field devices at the node

location. Possibly several nodes might drop out simultaneously due to an area

power failure. Network designers should become familiar with typical latency times

for reconstituting the network with the remaining nodes, and should provide

approximate methods of handling them in their application programs.


890 USE 100 00 November 2004 83

Latency Formulas

The formula for calculating node drop out latency (NDOL) produces two time values.

One time applies to nodes with addresses below the address of the drop-out node.

The 0ther time applies to nodes with addresses higher that of the drop-out node. (If

several nodes drop out simultaneously, the address of the lowest drop-out is used.

The formula used to calculate the NDOL for each node with an address lower thn

that of the lowest drop-out node is abbreviated NDOL(L), where (L)is the address of

any remaining node:

NDOL(l)= 80 + 4(lowest node address) + (qty of nodes remaining - 1) + 5(quantity of

nodes dropped - 1)

The formula used to calculate the NDOL for each node with an address higher than

that of the lowest drop-out node is abbreviated NDOL(H)where(H)is the address of

any remaining node:

The resulting times for both NDOL(L)and NDOL(H)are in ms.

The figure below summarizes the use of the two NDOL formulas.

CPU

Modbus Plus network

CPU CPUCPU CPUCPU

2 3 7 9 10 12

NDOL(L)NDOL(L)

node

drops out

NDOL(L) = 80 + 4(lowest node address) + (qty of nodes remaining - 1) + 5(qty of nodes dropped - 1NDOL(H) = NDOL (L) + (one token rotation time)


84 890 USE 100 00 November 2004

Estimating Latency for a Small Network

Overview Here is an example of estimating drop-out latency in a small network of

programmable controller nodes. Transfer of specific input and specific output data

is used. The network is structured as follows.

! 10 nodes, programmable controllers addressed 2... 11.

! Node 2 has an output of 2 registers to each of the other nine nodes (a total of 2 *

9 = 18 registers).

! Nodes 3... 1 each will input 2 registers and output 2 registers.

! Scan time of each controller is 10 ms.

Normal

Transaction

Time

The example above shows the normal response time for a transaction from node 11

to node 2, which is processed by node 2 and then returned to node 11. A similar

transaction is shown between nodes 9 and 2.

Abnormal

Transaction Time Due to

Node Dropout

The example above shows the abnormal time for the same two transactions in the

case of node 10 dropping out while node 11 holds the token.


890 USE 100 00 November 2004 85

Times Calculated The example above includes the calculation of:

! token transmission time for any node to transmit its data during the token pass

(TTT(n))

! token rotation time (TTR)

! low and high node dropout latency times (NDOL(L) and NDOL (H))

! normal response times (minimum and maximum) for communication between

two nodes before a drop-out occurs (TN(n))

! abnormal response time (minimum and maximum) between the same two nodes

with the latency interval included (TA(n))

Token transmission time is calculated as:

TTT(n) = (token pass time + specific output time + .001(quantity of nodes

communicated * quantity of registers * 16)

such that:

TTT(2) = (.530 +.530 +.001(1 * 2 * 16) = 1.348 ms

TTT(3...11) = (.530 +.530 +.001(1 * 2 * 16) = 1.092 ms

Token rotation time is calculated as:

TRT = TTT(2) + 9(TTT(3...11) = 11.18

A normal minimum response time for node 9 is calculated as:

TN(9) = (1 scan of node 9) + TTT(9) + (1 scan node 2) + TTT(2) = 10 + 1.092 + 10 +

1.348 = 22.44

TN for node 11 (TN(11)) is calculated the same way as node 9.

A normal maximum response time for node 9 is calculated as:

TN(9) = (1 scan node 9) + 2(TRT) + (2 scans node 2) = 10 + 2(11.18) + 20

= 52.36 ms

TN(11) = same as node 9

Node 10 drops out, causing the following latencies:

NDOL(9) = 80 + 4(2) + (9 - 1) + 5(1 - 1) = 96 ms

NDOL(11) = NDOL(9) + 11.18 = 107.18 ms

The dropout would create these abnormal minimum response times:

TA(9) = 22.44 + 96 = 118.44 ms

TA(11) = 22.44 + 107.18 = 129.62 ms

The dropout would create these abnormal maximum response times:

TA (9) = 52.36 + 96 = 148.36 ms

TA(11) = 52.36 + 107.18 = 159.54 ms


86 890 USE 100 00 November 2004

Estimating Latency for a Large Network

Overview Here is an example of estimating dropout latency in a large network of PLC nodes.

Peer cop is used to transfer specific input and specific output data. The network is

structured as follows:

! 32 nodes, PLCs addressed 2 ... 33

! nodes 2 and 3 act as masters, each controlling 15 slave nodes

! each master sends a total of 480 wordsó 32 words to each of its slave nodes

! each slave sends 32 words to its respective master

! scan time of each master is 30 ms; scan time of each slave is 15 ms

Normal

Transaction

Time

The example above shows the normal response time for a transaction from node 31

to its master node, which is processed by the master and then returned to node 31.

The example also shows a similar transaction between node 33 and its master node.

Abnormal

Transaction Time Due to

Node Dropout

The example above shows the abnormal time for the same two transactions in the

case of node 32 dropping out while node 33 holds the token.


890 USE 100 00 November 2004 87

Times Calculated The example includes the calculation of the following times:

! token transmission time for any node to transmit its data during the token pass

(TTT(n))

! token rotation time (TTR)

! low and high node dropout latency times (NDOL(L) and NDOL (H))

! normal response times (minimum and maximum) for communication between

two nodes before a drop-out occurs (TN(n))

! abnormal response time (minimum and maximum) between the same two nodes

with the latency interval included (TA(n))

Token transmission time is calculated as:

TTT (n) = (token pass time: + specific output time +.001 (qty of nodes communicated

* qty of registers* 16)

Such that:

TTT(master) = (.530 +.530 +.001(15 * 32 * 16) = 8.74 ms

TTT(slave) = (.530 +.530 +.001(1 * 32 * 16) = 1.57 ms

TRT = 2(TTT(master)) + 30(TTT(slave)) = 64.52 ms

A normal minimum response time for node n is calculated as:

TN(slave) = (1 scan master node) +TTT (master) + (1 scan slave node) + TTT(slave) =

30 + 8.74 + 15 + 1.57 = 55.31 ms

nodes 31 and 33 have this minimum normal response time.

a normal maximum response time for node n is calculated as:

TN(slave) = (1 scan master node) + 2(TRT) + (2 scans slave node) = 30 + 2(64.52) +

30 = 189.04 ms

Nodes 31 and 33 have this maximum normal response time.

Node 32 drops out, causing the following latencies:

NDOL(31) = 80 + (4)2 + (31-1) + 5(1-1) = 118.0 ms

NDOL(33) = NDOL(31) + 64.52 = 182.52 ms

The dropout would create these abnormal minimum response times:

TA(31) = 55.31 + 118.0 = 173.31 ms

TA(33) = 55.31 + 182.52 = 237.83 ms

The dropout would create these abnormal maximum response times:

TA(31) = 189.04 + 118.0 = 307.04 ms

TA(33) = 189.04 + 182.52 = 371.56 ms


88 890 USE 100 00 November 2004

Planning for Ring Join Time

Overview Nodes can be connected to the network while it is active, dynamically joining into the

address sequence. A node that was previously inactive due to a power-down state

can join the active ring upon its power-up. The network automatically senses the

presence of the new node and begins to include it in the address sequence.

In most cases a node joins under the direct control of the user - for example, when

a new node is connected to the network cable, or when a connected node has been

without power, and is then manually powered up. This case is illustrated in the figure

below.

The amount of time that is required for a node to join the address sequence (the ring)

is a function of a message counter and next-try node address that are maintained

mutually by all nodes that are present. The count and next-try address are passed

with the token from node to node.

For a given node, the counter increments with each message that is sent by the

node. Only when the counter reaches a value of at least 64 does the node invite the

node with the next-try address to join, at which time the message counter is reset to

zero. The next-try address is incremented with each attempt to allow a new node to

join. Neither the counter nor the ënext-tryí address are accessible to the user

application.

For example, consider the network shown in the figure above. Node 40 has been

absent, and is ready to join now. Regardless of which node holds the token, only

when the network message counter reaches 64 and the next-try address reaches

40 will the current node invite node 40 to join the ring. as node 40 joins, all other

nodes will add its address to their member list. However, each time a next-try node

address is invited to join and does not do so, approximately 2 ms must elapse before

its absence can be assumed and the token passed to the next node.

The worst case events occur when node 64 wants to join at the moment the node

that currently holds the token has a message count of 1 and a next-try address of 1

also. a minimum of 64 x 64 messages must pass before node 64 can be invited to

join.

The average latency for this case is approximately 6... 7s. Worst-case time is

approximately 15 s. Because the actual timing is beyond the direct control of the

application, the network planner should provide for worst-case timing to handle the

event of a new node joining the ring.

CPU CPUCPU CPU CPUCPU

1 20 30 40 50 64

Modbus Plus network

new mode to join


890 USE 100 00 November 2004 89

Adding or Deleting Nodes

When you plan your network application you should provide adequate safeguards

for the effects of nodes dropping out and rejoining the network ring. You can provide

programming in each nodeís application that will safely suspend the nodeís activity,

or that causes an orderly shutdown of the processes controlled by the node.

You should consider the inclusion of a dedicated node that monitors the network

activity and reports on the status of your application. This can assist you in

determining the origin of a condition in which several nodes are programmed to shut

down if proper data is not received from one or more other nodes. With the

monitoring node, you can more easily identify the node which started the shutdown

sequence.

If you use one or more spare (open) drop cables and connectors at selected sites

as points for temporarily connecting a network monitoring device, you should be

aware of the effects on network timing when you add or delete that device on an

active network. Adding the new node causes an increase in the networkís token

rotation time, reducing the overall data throughput. Deleting the node causes

dropout latency times.

NETWORK TIMING

Before you connect or disconnect any devices on an active network, you should be

aware of its effect on network timing. Use the formulas in this chapter to estimate

your networkís token rotation time, data throughput, and node dropout latency time.

Apply sufficient margin to your timing to provide for worst-case conditions, such as

multiple nodes leaving or rejoining the network due to area power faults.


CAUTION


90 890 USE 100 00 November 2004

Precautions for Hot Standby Layouts

Overview A case exists in which a node can leave the network and rejoin it without the control

of the user application. This can occur when two nodes are connected in a hot

standby configuration, as shown in the figure below.

Programmable controllers connected in hot standby each have a network address.

Both nodes are active, with the two addresses offset by 32, as shown in the figure

above. As long as no transfer occurs between the primary and secondary

controllers, the token is passed in the networkís usual ascending address sequence.

If a hot standby transfer occurs, CPU B assumes the primary role and CPU A

becomes the secondary. To maintain consistency in application programming

among the nodes, CPUs A and B must also exchange node addresses. For this to

occur, both nodes must momentarily leave the network and then rejoin it after the

transfer has taken place. At that point CPU B (the new primary) then continues as

node address 4, handling its traffic with the other nodes in the manner that you

programmed for node 4.

Both nodes must e separately invited to rejoin through the ring-join process outlined

on the previous page. This requires the use of an internal message counter and

next-try address that are maintained by the network nodes and which are beyond

the control of the user application.

Note: In the worst-case timing for his event, as much as 15 s can be required for

the ring to be reconstituted with the nodes in place at their new addresses. This can

occur in a network of any size, if node address 64 is one of the nodes attempting

to join at the same moment that the message counter and next-try addresses are

both at a value of 1.

In most cases the time will be significantly less than this maximum amount,

however the network planner should account for this worst-case event in the

design of the network layout and programming of the node applications.

CPU CPUCPUCPU A

CPU

1 2 3 4 36 5

Modbus Plus network

primary

CPU B

secondary

hot standby configuration


890 USE 100 00 November 2004 91

Guidelines for a Single Network

Using MSTR

Functions

Each controller on the network should have a maximum of four MSTR functions

active at the same time. Plan to have an MSTR function transferring large quantities

of registers (up to 100 maximum per MSTR), rather than multiple MSTRs

transferring small amounts of registers. You can easily use block instructions in your

ladder logic program to produce the block of contiguous registers required for each

MSTR.

Here are two timing examples, which are taken from a network with 16 nodes

without global data being passed.

! Every node has four MSTR functions active at all times. Each MSTR is writing 50

registers. The average token rotation time is 193 ms

! Every node has two MSTR function active at all times. Each MSTR is writing 100

registers. The averagetoken rotation time is 126 ms.

Using Peer-to-

Peer

Communication Techniques

Use peer-to-peer passing of data where applicable, rather than master-slave polling.

For example, in a master-slave process, you can have a user interface device

perform polling of your process control devices to determine if status updates are

necessary. Using a peer-to-peer technique, you can have each process device

initiate messages to the user interface device as events happen in the process. This

reduces the total quantity of transactions on the network, improving network

performance.

Destination devices must be able to sense the presence of new data and handle it

before more data is received. One way to do this is to have each destination device

maintain a write status register for each other device that can originate data to that

application. When new data is sent, this status register is written into in addition to

the data registers that are written. A new data ready sentinel bit can be set by the

write operation and can be reset by the local application when the data is extracted

and used. Other bits in the status register can indicate the data block length, target

task, and other information. Additional registers ca be used for this purpose if

required.

The destination deviceís software can handle missed events internally on a timeout

basis, rather than by polling, and still manage orderly shutdowns. Plan your

application from the start to use effective techniques for throughput.

Note: The same total quantity of data is being moved in the two examples. By using

fewer MSTRs to move the data, the second example gives a 67 ms (about 35%)

improvement in the average token rotation time.


92 890 USE 100 00 November 2004

Using the Global Database

You can broadcast up to 32 registers using the networkís global database, with up

to 64 nodes receiving this data during the current token pass. This can be most

effective in data acquisition and alarm handling, in which many devices can react

quickly to a single transmission of data.

The MSTR write global database function executes upon release of the token by the

initiating node. The MSTR read global database function executes during the scan

of each receiving node, making the data available immediately to the nodeís

application.

Security Considerations

in Node

Addressing

Modbus Plus nodes can be addressed within the range 1 ... 64 decimal. For security

purposes, consider limiting the range to between 2 and 64. (You probably will not

require all 64 addresses on a single network.)

In non-networked applications, many users have traditionally attached to a local

controller by identifying it as device 1. If a person tried to do this with a controller

operating in its bridge mode, a remote controller at node address 1 could be

attached and possibly started, stopped, or programmed. Avoiding the use of

address 1 prevents inadvertent attaches by persons who may be unfamiliar with a

controllerís bridge mode.

Selecting Node

Addresses for

Best Throughput

Consider assigning network node addresses to the various devices in a manner that

supports efficient message handling. If your network consists of multiple nodes with

heavy traffic occurring at one node, your choice of node addressing can affect the

token rotation time and data rate.

For example, consider a network of 12 nodes, with an average token rotation time

of 100 ms. The nodes are addressed from 2 ... 13, with no gaps in the address

sequence. In the application, nodes 2 and 3 are initiating many transactions to node

4. As the token passes to node 4, that node might not have had enough time to scan

and process all of its message traffic. Node 4 might have to wait for a later rotation

of the token in order to send its data responses to the initiating nodes.

By assigning a higher node address to the receiving node, for example address 12,

the device can use the time during which the token is passing through the other

nodes to process its traffic. By the time the token arrives, a data response can be

ready.

The time saved in each transaction is the difference between the time for a

full rotation (nodes 2,3,4 ... 13, 2, 3, 4) and the time for a partial rotation

(nodes 2,3 ... 12).


890 USE 100 00 November 2004 93

Consistency in Node

Addressing

Use a consistent method for identifying node addresses. This will facilitate

development of your application program and make future expansion easier to plan.

For example, use addresses in the range 20 ... 29 for bridges, and addresses in the

30s for host-based network adapters.

Using addresses 20 ... 24 for bridge plus devices, with addresses 2 ... 9 for

controllers, allows you to use implicit addressing in your applications. For examples

of message routing using this and other addressing methods, see message routing

(see p. 171).

Remote

Programming

Online programming of nodes while network data transactions are in progress does

not reduce the networkís data transfer rate. Devices maintain program master and

slave paths that are separate from their data paths. Some programming commands,

like the search command, do increase the scan time of controllers. When these

commands are being executed, the data rate (registers per second for active MSTR

functions) may be reduced in the controller.

For security, the memory protect keyswitch on programming panels should always

be set to the on position when programming is not in progress.

Controlling the

Sequencing of MSTR Functions

When you use multiple MSTR functions in a controller, each MSTR acquires its own

data master path which is maintained open until its transaction terminates. The

paths are independent of each other. A transaction can be started on one path, and

another transaction can be started some time later on a second path. Their

completions are determined by other devices on the network.

If your application needs to complete the MSTR functions sequentially, use logic to

monitor the complete outputs before enabling other MSTR functions.

Optimizing Node

Counts

Consider separating a device application into two or more devices to avoid queuing.

For example, if you expect heavy queuing within one controller because of a high

concentration of traffic from other nodes, consider employing two nodes instead.

Although the additional node count adds slightly to the token rotation time, the

opportunity for parallel processing without queuing makes data available more

quickly as the token is received in each of the two nodes.

Note: You can use the same network address at both network ports of a bridge

plus. When using hot standby controllers, remember the address offset of 32

between the primary and standby unit. Avoid duplicating addresses on the same

network.


94 890 USE 100 00 November 2004

Prioritizing and Compressing

Data

Plan the data transactions in your application so that only needed information is

sent. Process the data before transmission, condensing it into larger messages if

possible. Reduce the amount of data messages to be sent, or reduce the frequency

at which they have to be sent.

Schedule the data to be sent on a timed basis rather than on every scan of a

controller to reduce the loading on the network. Time the transmissions to the

intervals at which the receiving device needs the information.

Selecting Bridge

Multiplexer Port Modes

The four Modbus ports on bridge multiplexers can be separately configured for

either ASCII or RTU communications. RTU mode provides significantly better

throughput than ASCII for a given baud rate. Plan to configure the ports for RTU

mode, using the highest baud rate possible for your Modbus devices.


890 USE 100 00 November 2004 95

Guidelines for Multiple Networks

Overview If your applicationís data rate requirements are not met between nodes on a single

network, consider the use of bridges to join smaller networks. The grouping of nodes

on each network requires determination of which nodes must communicate at high

data rates with other nodes.

Modbus Plus networks that are joined by bridges will have separate token rotations.

When a message passes through a bridge to another network, the other networkís

token rotation time will be a factor in communication timing. In general, messages

sent through bridges will take longer to complete than messages sent between

nodes on a single network.

Note: Global data is not passed through bridges.

Peer cop and distributed I/O (DIO) data is transacted on a single network only. It

does not pass though bridges. Bridges are not applicable to networks employing

peer cop data transfers, nor to networks in DIO applications.


96 890 USE 100 00 November 2004

Bridge Communication

Paths

The figure below shows the structure of communication paths within a bridge. It

illustrates the amount of paths that are available in each direction.

The bridge contains eight independent data master paths and eight independent

data slave paths for each of its two ports. Messages received at the network A port

with destinations on network B or beyond are given data slave paths on network A,

and then passed to data master paths at the network B port. In the other direction,

incoming messages at network B are given data slave paths at that port and data

master paths at network A.

As each message is allocated one slave path and one master path in the bridge, up

to eight messages can be routed from each network to the other without queuing.

When all eight paths are in used in a given direction, other incoming messages will

queue in the bridge, unless they have previously been routed through another

bridge. Messages that have already been passed through a bridge will cause an

error response when they are received at the second bridge. The error response will

be returned to the error status register of the originating MSTR function and can be

tested by the application program. This prevents tieing up paths in the originating

device due to excessive queuing. MSTRs can be temporarily released (using their

ABORT inputs), and their data master paths given to other MSTRs.

BP85 bridge plus

network A network B

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DS

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM

DM


890 USE 100 00 November 2004 97

Using Multiple Bridges Between

Networks

If your application will have heavy traffic between networks, you can use two or more

bridges to increase the number of paths and to reduce or eliminate queuing. The

figure below shows an example.

You can plan your application so that high priority messages are passed through a

dedicated bridge. Design the message flow so that the bridge always has available

paths. Low priority messages can be allowed to queue in the other bridge.

Note: Data master paths will remain busy in the originating nodes while messages

are queued in the bridge.

node node node node

node node node node

bridge bridge

network A

network B

high priority low priority


98 890 USE 100 00 November 2004

Sample Communications Across Networks

Overview The figure below shows two controllers on separate Modbus Plus networks joined

by a bridge. Each controller has its own peer processor. The bridge has a separate

peer processor for each network. Each network has a separate token rotation

pattern and timing.

During the ladder logic scan in unit A, an MSTR block is executed that specifies a

read request to unit B. At the end of the block execution, the read request is sent to

the peer processor in unit A. The following events occur.

Step Action Result

1 When the peer processor in unit A acquires

the network token, it transmits a read

request.

The peer processor in the bridge

sends an immediate

acknowledgement.

2 When the bridge has the token on network

B, it transmits the read request to unit B.

The peer processor in unit B sends

an immediate acknowledgement to

the bridge.

3 At the end of the ladder logic scan in unit B,

the incoming transactions are handled.

The peer processor in unit B is ready

with the data response to the read

request.

4 When the peer processor in unit B acquires

the token, it sends the data response to the

bridge.

The peer processor in the bridge

sends an immediate

acknowledgement.

5 When the bridge has the token on network

A. It transmits the data response to unit A.

The peer processor in unit A sends

an immediate acknowledgement.

6 At the end of the ladder logic scan in unit A,

the incoming transactions are handled. The

transaction is complete at the next solve

time of the MSTR function in unit A.

Data registers will be written, and the

MSTR functionís complete output

goes on.

controller

A

peer

processor

controller

B

peer

processor

request

response

peer

processor peer

processor request

response

network A network B

bridge


890 USE 100 00 November 2004 99


If the scan time in unit B is much shorter than the token rotation time, unit B can

create the data response and have it ready before the token reaches unit Bís peer

processor. On the other hand, if a data path is not free in either the bridge or n unit

B, the request will be queued by that unitís peer processor and will wait until a path

is free.


1 0... 1 token rotation, net A 1/2 token rotation, net A 1 token rotation, net A

2 0... 1 token rotation, net B 1/2 token rotation, net B 1 token rotation, net B

3 0... 1 scan, unit B 1/2 scan, unit B 1 scan, unit B

4 0... 1 token rotation, net B 1/2 token rotation, net B 1 token rotation, net B

5 0... 1 token rotation, net A 1/2 token rotation, net A 1token rotation, net A

6 0... 2 scans, unit A 1 scan, unit A 2 scans, unit A


100 890 USE 100 00 November 2004

A Summary of Network Planning

Analyzing Your Needs

Analyze your applicationís data communication requirements prior to laying out your

network or writing your programming. Make a simple chart to guide your planning.

Include the following items for each communication:

Finding

Opportunities for

Increasing Performance

As you enter your needs on your planning chart, look for the following opportunities

to improve performance by reducing network loading:

! Carefully examine the purpose of each communication and group of registers to

ensure that the communication and data are needed.

! Try to group multiple communications between two nodes into fewer

transactions.

! Try to reduce the frequency at which reads or writes are enabled. Remember that

the maximum frequency of enabling MSTRs is once per scan.

! Look for receiving controller nodes that have more than four potential

transactions being sent to them; these nodes might have queuing. Look for types

of communication that have high priority and that are sent to nodes that might

have queuing.

! Use peer-to-peer passing of data where applicable, rather than master-slave

polling.

! Reduce queuing by reducing the number of communications to a controller node

or reducing the frequency of enabling communications so that only four reads or

writes are handled by the receiving controller. Consider having the receiving node

originate some transactions; this will use its data master paths, freeing data slave

paths.

Originating Node network number

node address

device description

device type

Receiving Node network number

node address

device description

device type

Communication purpose

priority

sent under what conditions

frequency of enabling

number of registers

response time needed

890 USE 100 00 November 2004 101

4Documenting the Network Layout

At a Glance

Overview This chapter discusses ducumenting the network layout.



Topic Page

Documenting Your Network Layout 102

Worksheets for Network Planning 103

Defining Your Node Requirements 104

Topology Planning Worksheet 106

Estimating Cable Lengths 108

Reviewing Your Topology Plan 109

Detailing the Network Layout 110

Network Planning Worksheet 112

Cable Routing Worksheet 115

Materials Summary Worksheet 118

Documenting the Network Layout

102 890 USE 100 00 November 2004

Documenting Your Network Layout

Overview Your planning should include the preparation of documents that describe your

network node requirements, setup parameters, installation materials, cable routing,

and labeling. Provide information to support the following kinds of activity.

! ordering the proper types and quantities of node devices and network materials

! routing and installing the network cable

! identifying, labeling, and installing the network components

! setting up the network addresses and other device parameters

! expanding, modifying, and servicing the network and network devices


890 USE 100 00 November 2004 103

Worksheets for Network Planning

Overview Five kinds of worksheets are provided in this book to assist you in your network

planning. This chapter shows examples of their use.

See p. 183 for blank worksheets. You can make photocopies as needed for

documenting your network layout. Some copiers can enlarge the size of the sheets

if that is more suitable.

Here are the five types of worksheets.

Type of Worksheet Description

node planning Use this sheet to list the communications requirements and setup

parameters of each node device in your application

topology planning Use this sheet to define each networkís layout and the

interconnection of multiple networks.

network planning Use this sheet to itemize the trunk cable length, tap, drop cable,

and labeling requirements at each node site.

cable routing Use this sheet to show the routing of the network trunk cable

through the node sites in your facility.

materials summary Use this sheet to summarize your network devices, cable

components, supporting materials, and tool requirements for

ordering purposes.


104 890 USE 100 00 November 2004

Defining Your Node Requirements

Overview Before you document your network layout, make a list of your requirements for each

node device. Include the node address, device type, site location, application, setup

parameters, and a summary of the communications to be sent and received.

Include all the necessary setup parameters for each type of device. For example, if

the device is a controller, define its free-running timer location to identify the

registers that will be used for Modbus address mapping. For a host-based network

adapter, define its memory base address and driver parameters. For a bridge

multiplexer, define its attached Modbus device, Modbus port parameters, and

Modbus address mapping.

An example of a node planning worksheet is shown in the figure below. You can

adapt this worksheet to your requirements, adding other fields of information as

needed. If a node has several applications, you may want to use separate

worksheets for showing the types of communication that will be used in each

application.


890 USE 100 00 November 2004 105

When you have defined each nodeís requirements, use the network worksheets in

the rest of this chapter to document your network layout, cable routing, and

materials.

Modbus Plus Network

Node Planning Worksheet

Facility/Area:

Network Number:

Node Address:

Project Name:

Project Engr:

Maintenance:

Date:

Tel:

Tel:

1

2

paint mod #1

p. green

v. white

6-6-96

2742

3824

1. Device:

Type

CPU 213 03

Description

programmable controller

Site Location

paint #1 panel 5A

2. Application:

paint mod #1

3. Setup Parameters:

N/A

4. Communications Originated:

Network

111

31010

112

init loadparams 1params 2

read dataread dataread data

50 regs100 regs75 regs

150 ms.250 ms.200 ms.

5. Communications Received:

11

310

12

alarmsproc stats

read globalread data

16 regs50 regs

50 ms.100 ms.

Notes:

Priority Purpose Type of Communication Amount of Data Response Time NeededNode

Network Priority Purpose Type of Communication Amount of Data Response Time NeededNode


106 890 USE 100 00 November 2004

Topology Planning Worksheet

Overview The figure below is an example of a completed topology planning worksheet. The

example shows two networks that are interconnected by a BP85 bridge plus. Each

deviceís network node address, type, application, and site location are listed.

Top of Worksheet

If applicable, identify the plant facility or area, network, and project. Show how to

contact the responsible project engineer and maintenance person.

Network Topology Area

Lay each network out in a linear path for clarity. Use an end symbol to show the two

physical ends of each network section. Make four entries to identify each node

device.

Use the following legend.

Entry Number Entry Content Description

first node number the deviceís address on the network

second device type the deviceís model number

third application the title of the deviceís application or use

fourth location the deviceís site location in your facility


890 USE 100 00 November 2004 107

Use additional entries as needed to further identify each node in your application.

Modbus Plus Network

Topology Planning Worksheet

Facility/Area: paint Project Name: mode #1 Date: 6-6-96

Project Engr: P. Green Tel: 2742

Maintenance: V. White Tel: 3824

END END

2

CPU 213 03

paint mod # 1

paint #1

3

SA85

paint UI

paint #2

N/A

Service Port

N/A

paint #2

10

CPU 213 03

paint mod #1

paint #3

23

BP85

N/A

paint #3

22

END

END

N/A

RR85

N/A

trans #4

6

CPU 213 03

trans line

trans #1

10

SA85

trans UI

trans #2

12

CPU 113 03

Interlocking

trans #3

END

ENDN/A

Service Port

N/A

paint #5

First Entry:

Second Entry:

Third Entry:

Fourth Entry:

Legend: Node Number

Device Type

Application

Location

END End site of network section

Notes:

25

BM85

N/A

trans #5


108 890 USE 100 00 November 2004

Estimating Cable Lengths

Overview After defining the network topology, consider the required cable lengths between

nodes. You can enter the estimated cable length onto the topology planning

worksheet. This information will be required for the detailed planning worksheet you

will be using next.

For dual-cable network planning, note that the point of the two cable runs is to

minimize the potential for communication loss through interference or damage to

either cable. Therefore you should plan for proper physical separation of the cables

at all points except for where they connect to a network node device.

Use a facility grid or floor plan to estimate the cable lengths. Account for all

horizontal runs, vertical rises, and required clearances from interference sources. A

walkthrough to confirm your estimate is best.


890 USE 100 00 November 2004 109

Reviewing Your Topology Plan

Overview Review the topology planning worksheet after estimating the cable lengths. Revise

it if necessary to account for the minimum and maximum cable length requirements.

For example, if there is an estimated cable length of less than 10 ft. (3 m) between

a pair of nodes, revise the plan to meet this minimum length requirement.

If there is an estimated a distance of more than 1500 ft. (450 m) between two nodes

or if you are using more than 32 nodes on one cable section, revise the plan to

include at least one RR85 repeater device in the cable path.

Once the topology planning is completed, proceed to the detailed worksheets in the

rest of this chapter.


110 890 USE 100 00 November 2004

Detailing the Network Layout

Overview There are three worksheets to document detailed planning. Examples are described

below.

The table below describes the the three worksheets.

Type of Worksheet Description

network planning This worksheet details the layout of the network: cable lengths, taps,

node devices, labeling of panels, cables, and connectors.

cable routing This worksheet details the routing of your cables through the sites of

your plant facility.

materials summary This worksheet summarizes the network materials requirements

before placing orders: node deviceís, trunk cable, drop cables, taps,

labels, installation hardware, tools, and test equipment.


890 USE 100 00 November 2004 111

Modbus Plus Network

Network Planning Worksheet

Modbus Plus Network

Cable Routing Worksheet

Modbus Plus Network

Materials Summary Worksheet

Facility/Area:

Network Number: Cable: A B

Sheet: Of

Sites: To

Project Name: Date:

Project Engr. Tel:

Maintenance Tel:

Site#

1. Site Labeling:

1A Name of site location:1B Plant site coordinates:1C Enclosure number:1D Panel label:1E Device label:

Facility/Area:

Network Number: Cable: A B

Sheet: Of

Sites: To Scale: Horiz: Vert:

Project Name: Date:

Project Engr: Tel:

Maintenance: Tel:

1

A B C D E F

Facility/Area:

Network Number:

Project Name: Date:

Project Engr: Tel:

Maintenance: Tel:

Description Part Number Manufacturer QTY

Used

QTY

Spare

QTY

Total

Unit of

Measure

Date

Ordered

Date

Received

1. Network Devices:

RR85 Repeater ModiconBP85 Bridge Plus Modicon

BM85 Bridge Multiplexer Modicon

Progcontroller Modicon


112 890 USE 100 00 November 2004


Overview Each network planning worksheet can document up to eight sites. Use additional

worksheets as required. The figure below is an example of a completed network

planning sheet. The example shows a network of four nodes. (two controllers, one

SA85 network adapter, and one BP85 bridge plus), plus one additional tap and drop

cable for future service access.

Use this worksheet for a single cable network, each cable on a dual cable network,

or both cables on a dual cable network.

Top of Worksheet



Site Labeling Provide a labeling method for identifying network components. Enter site names into

line 1A, such as department names or floor/room numbers. If a grid locator system

is used, enter site coordinates into line 1B. If a device enclosure or cabinet is used,

identify it in line 1C. Enter further information into lines 1D through 1G to identify

each siteís mounting panel, device, and incoming/outgoing cable runs.

Network Type/

Cable Type

Description

single cable network Enter the complete information in all areas of the sheet.

each cable on a dual

cable network

Use a separate planning sheet for each cable. Check cable A or cable

B as appropriate in the top area of the sheet. Enter the site labeling

and cable length information for the cable. In the device type area,

enter the network device types (except for RR85 repeaters) only once

on the cable A sheet. Enter the RR85 repeaters on both sheets.

(RR85 repeaters are used on both cables.)

both cables on a dual

cable network

Check both cable A and cable B in the top area of the sheet. In the

site labeling area. Use a labeling method that will properly identify

each cable. In the cable length area, make sure to enter the total

length for both cables, including the service loops on both cables.


890 USE 100 00 November 2004 113

Trunk Cables and Taps

Estimate the length of the cable between sites. Each segment except the first has a

cable run from the previous site (line 2A). A service loop is included (line 2B) to

eliminate pulling or twisting of the cable. Include all vertical routing (such as runs

between for levels) and all horizontal routing (such as bends around ventilating

shafts). Add these lengths, and enter their total into 2C. Multiply this by 1.1

(providing an additional 10 percent) for finished dressing of the cable, and enter this

final length into line 2D. This is the cut length for each segment.

Make sure that the minimum length that will result between any pair of nodes will be

10 ft (3 m) or more. Make sure that the combined lengths between all nodes on a

cable section will be 1500 ft (450 m) or less.

Enter an X into line 2E for each site showing that a tap is to installed. At the two end

sites on the network section, enter an X into line 2F to show that the tapís termination

jumpers are to be installed

Drop Cables Enter an X into line 3A or 3B for the drop cables at each site. Ensure that the drop

cable is long enough to allow a service loop for maintenance.

Device Type Specify the device to be installed at each site. For programmable controllers, enter

the model number into line 4E. For host network adapters enter the model number

(SA85, SM85, etc.) into 4F. For other devices, enter the model number or an X into

the appropriate line (4A through 4K) for each site. Include at least one access point

(line 4A) at a convenient site for future service.


114 890 USE 100 00 November 2004

Modbus Plus Network


Facility/Area: paint Project Name: mode #1 Date: 6-6-96

Project Engr: P. Green Tel: 2742

Maintenance: V. White Tel: 3824

Notes:

Network Number: 1 Cable: A B

Sheet: 1 Of 1 NOTE: 2.

Sites: 1 To 5 Site# 1 2 3 4 5

1. Site Labeling: Paint Paint Paint Paint Paint 1A Name of site location: #1 #2 #3 #4 #5 1B Plant site coordinates: B5 B3 B3 C2 C2 1C Enclosure Number: N/A N/A N/A N/A N/A 1D Panel Label: 5A 6A 6C 12A 12A 1E Device Label: 5A1 6A3 N/A 12A2 12A3 1F Cable from previous site label: N/A 6A3A 6C3A 12A2A 12A3A 1G Cable to next site label: 5A1AA 6A3AA 6C3AA 12A2AA 12A3AA

2. Trunk Cable and Taps: 2A Cable run from previous site, length: N/A 160 58 140 25 2B Service loop at this site (2M/6ft): N/A 6 6 6 6 2C Run length (Sum of 2A and 2B): N/A 166 64 146 31 2D Cut length (multiply 2C times 1.1): N/A 183 71 161 35 2E Tap.990NAD23000: X X X X X 2F Termination jumpers installed in tap X X

3. Drop Cables: 3A Drop Cable, 2.4M/8FT, 990NAD21110: X X 3B Drop Cable, 6M/20FT, 990NAD21130: X X X

4. Device Type:

4A Service access point connector: X 4B RR85 repeater: 4C BM85 bridge multiplexer: 4D BP85 bridge plus: X note 1 4E programmable controller (model no.): 213.03 213.03 4F Host network adapter (model no.): SA85 4G Network option module (model no.): 4H DIO drop adapter (model no.): 4I TIO module (module no.): 4J 4K

1. Site 5:

2. Cables:

BP85 connects between networks #1 and #2.Count only once in materials summary.

This worksheet shows cable lengths for cable A.Use separate worksheet for cable B.


890 USE 100 00 November 2004 115

Cable Routing Worksheet

Overview Whenever possible, obtain a site layout for your plant facility and use it to plot your

network cable routing. If no drawing is available, use the cable routing worksheet in

this guide. Adapt the blank worksheet (see p. 183) as needed for your network cable

path.

The figure below shows an example of a completed cable routing worksheet. The

example shows a network of four nodes, plus one additional connector for future

service access. The site location correspond to those shown on the network

planning worksheet.

You can use this worksheet for a single-cable network, each cable on a dual-cable

network, or both cables on a dual-cable network.

Top of

Worksheet



You can enter grid scale dimensions at the top of the worksheet to plot your cable

routing. You can use separate dimensions horizontally (grids A ... F) and vertically

(grids 1 ... 5). For example, each grid can represent a square site area such as 10

m x 10 m, or a rectangular area such as 10 m x 50 m. If you wish, you can leave the

scale blank and mark each cable run length directly onto the worksheet.

You can also make multiple copies of this worksheet, and use a relatively small

scale on some sheets to show local placement of devices and cables. Use a larger

scale on another sheet to show the overall network layout.

Type of Network

Cable Routing

Action

single-cable network Show the cable routing.

dual-cable network,

each cable

Use a separate planning sheet for each cable. Check cable A or cable

B as appropriate in the top area of the sheet. Show the cable routing.

You can use a different grid scale for each cable, if appropriate.

dual-cable network,

both cables

Check both cable A and cable B in the top area of the sheet. show the

cable routing for both cables. Make sure to mark the sheet so that

each cable (A or B) is properly identified over its entire run.


116 890 USE 100 00 November 2004

Worksheet Grid Area

Draw the cable routing path into these areas. Provide sufficient information to enable

installers to properly route the cable between site locations. The following type of

information will be useful.

! the area name or department of each site location to which the cable is to be

routed

! the identification label of the device enclosure, cabinet, or mounting panel at each

site location

! the identification label of the networked device at each site location

! the cable routing path between site locations

! the cable routing method, such as through new or existing cable troughs,

raceways, or conduits

! any additional cable installation information, such as separation from interference

sources, mounting of strain reliefs, and other methods of protecting the cable


890 USE 100 00 November 2004 117

Modbus Plus NetworkCable Routing Worksheet

Facility/Area:

Network Number

Project Name

Project Engr:

Maintenance

Date:

Tel:

Tel:

1

paint mod #1

P. Green

V. White

6-6-96

2742

3824

Notes:

Sheet: 1 Of 1 Note 4

Sites 1 To 5

2. Allow 3 ft. clearance between cable and air duct.3. All cables routed in overhead trays (existing).4. This sheet shows run for cable A. Use separate sheet for cable B.

A B C D E F

1

2

3

4

5

Scale: Horiz:

[12A]

paint #3

[12A]

5

4

3

2

1

paint #2

paint #1

[6C]

[6A]

[5A]

Note 2

Cable A__ B__

50 ft Vert. 50 ft

1. Local panel ID shown in brackets [ ].


118 890 USE 100 00 November 2004

Materials Summary Worksheet

Overview When your planning of the network layout and cable routing is complete, you can

use the materials summary worksheet to list the required components and start an

ordering process. Use the worksheet to list the types of materials, part numbers,

manufacturers/sources, and quantities to be ordered. Some items are already listed

to start your planning. Enter any additional items into the blank lines provided.

Use additional worksheets if more space is needed. If you are planning multiple

networks, you can use one worksheet for each network and then summarize your

requirements on a final worksheet.

Dual-Cable

Networks

Your final worksheet should contain the total of all materials you will be specifying

and ordering for both cable runs. Note that RR85 repeaters are used separately on

each cable. Where an RR85 is used between nodes on one cable run, another

RR85 must appear between the same nodes on the other cable run.

The figure below is an example of a completed materials summary worksheet. It lists

materials for a network of four nodes (two programmable controllers, one SA85

network adapter, and one BP85 bridge plus), plus one additional connector for future

service access. The example also shows provisions for service spares.

Top of

Worksheet




890 USE 100 00 November 2004 119

Network Device Summarize the devices that will be connected to the network. For programmable

controllers, list the model number and quantities of each type.

Avoid duplication when summarizing your device requirements. When you include

an RR85 repeater to join two network sections, make sure to count that device only

once.

Trunk Cable and

Taps

Summarize the amount of cable that will be required. Convert the network cable

length into standard reel lengths of 100, 500, or 1000 ft.

If cable will be ordered as two or more reels, specify reel lengths that will allow you

to run continuous cable segments between sites, without splices. On dual-cable

layouts, make sure that this requirement is met for each cable run.

Summarize the amount of taps that will be required.

Drop Cables Summarize the drop cables in each size that will be required.

Labels Summarize the types and quantities of labels that will be required to properly identify

the network components for installation and future servicing.

Installation

Hardware

Enter the types and quantities of hardware items that will be required to install,

secure, and support the network cable and devices.

Note: Separate RR85 repeaters are used on each cable on a dual-cable system.

When you include a BP85 bridge plus to join two networks, count the device only

once.


120 890 USE 100 00 November 2004

Tools/Test Equipment

Enter the types and quantities of tools and test equipment that will be required to

install and test the network.

Modbus Plus NetworkMaterials Summary Worksheet

Facility/Area:

Network Number:

Project Name:

Project Engr:

Maintenance:

Date:

Tel:

Tel:

1

note 1.

paint mod #1

P. Green

V. White

6-6-96

2742

3824

1. Network Devices

2. Trunk Cable and Taps (Note 2)

3. Drop Cables (Note 2)

4. Labels (Note 2)

5. Installation Hardware (Note 2)

Notes:

6. Tools/Test Equipment

RR85 repeaterBP85 bridge plusBM85 bridge multiplexerprogcontrollerhost network adapternetwork option moduleDIO drop adapterTIO module

ModiconModiconModiconModiconModiconModiconModiconModicon

eacheacheacheacheacheacheacheach

1

21

1

11

2

32

6-6-96

6-6-966-6-96

NW-BP85-002

CPU 213 03AM-SA85-002

MBplus trunk cableMBplus tap

ModiconModicon

490NAA27102990NAD23000

2

10

-

2

2

12reeleach

6-6-966-6-96

Modicon

Modicon

6-6-966-6-96

6-6-966-6-966-6-966-6-96

6-6-966-6-96

each

kit

kitkit

kit

4 1 5

6 1 7

lidco

lidcolidco

lidco

compsco

compsco

3 - 3

1 - 12 - 2

1 - 1

990NAD21110

990NAD21130

MBplus drop (2.4m/8ft)

MBplus drop (6m/20ft)

panel

device

cable

connector

R-321R-330R-787R-212

SR5-74

WC3-2436 4 4040 5 45clamps, wire

strain/wireeach

each

each

1. This sheet is for network #1. Use separate sheet for network #2.

2. Includes materials for both cables A and B.

890 USE 100 00 November 2004 121

5Installing the Network Cable

At a Glance

Overview This chapter discusses installing the network cable.



Topic Page

Overview of the Cable Installation 122

Tools and Test Equipment Required 123

Before You Start 124

Routing the Cables 125

Mounting the Taps 127

Connecting the Trunk Cables 128

Connecting the Drop Cables 131

Grounding 133

Labeling 134

Checking the Cable Installation 135

Installing the Network Cable

122 890 USE 100 00 November 2004

Overview of the Cable Installation

Overview This chapter describes how to install the network trunk and drop cables. It is

intended primarily for the installer, but can also be useful to the network planner in

estimating installation time and labor requirements. It also provides an overview of

tap connections to assist the network planner. Each tap package includes detailed

instructions for the tap installer.

Follow the steps below to install and check the cable.

Step Action

1 Install a tap at each network node site. Mount it close enough to the node device

to allow the drop cable to be installed with a sufficient service loop. Drop cables

are available in lengths of 2.5 m (8 ft.) and 6 m (20 ft.).

2 At each tap location, except the two ends of the section of trunk cable

(see p. 11), make sure that both internal jumpers are disconnected and removed

inside the tap.

3 At the tap locations at the two ends of the section of trunk cables, connect both

of the internal jumpers (see p. 128) inside the tap.

4 Route the trunk cable in accordance with the layout diagram (see p. 110), and

connect it to the taps. Include a small service loop at the tap connection to

eliminate any pulling or twisting of the cable.

5 Connect the proper length of drop cable to each tap. Connect the ground wire

on the drop cable to the tap grounding screw and node device panel ground.

6 Label the trunk cable segment and drop cables to assist in future maintenance.

7 Inspect the cable run and check the cableís continuity before connecting it to the

network node device.


890 USE 100 00 November 2004 123

Tools and Test Equipment Required

Overview The following tools and test equipment are required to install and check the network

components.

! Wire cutter to cut the cable segments.

! Wire stripper or knife to remove the cable jacket.

! Flat screwdriver for connecting the drop cable ground lugs.

! Insertion tool for pressing wires into the tap terminals. The tool is available from

AMP Incorporated, P.O. Box 3608, Harrisburg, PA 17105-3608 USA (part

number 552714-3) or your local Modicon product representative (part number

043509383).

! Ohmmeter for checking the cable continuity.

If possible, avoid the use of cable pulling tools by laying the cable directly into

overhead troughs or raceways. This will minimize potential stretching or cutting

damage. If a pulling tool is used, follow the manufacturerís guidelines and avoid

excessive force in pulling the cable.


124 890 USE 100 00 November 2004

Before You Start

Overview Before routing the cable you should have a cable routing diagram that shows:

! site locations of network node devices

! routing paths of each cable segment

! cable segment distances and cut lengths

! list of materials required (length of trunk cable, quantities of taps, drop cables,

cable ties, adhesive labels, and other materials as needed)

See p. 101 to prepare this diagram. If you cannot obtain such a diagram, you must

observe all the precautions described in this guide for physical and electrical

protection of the cable during installation.

POSSIBLE DEGRADED NETWORK PERFORANCE

Failure to provide proper physical protection of the cable can cause damage to the

cable conductors or insulation. Failure to provide proper electrical protection of the

cable can result in excessive interference induced from adjacent circuits. This can

cause degraded network performance.


CAUTION


890 USE 100 00 November 2004 125

Routing the Cables

Overview The figure below shows typical cable routing of the network trunk cable between tap

locations. The figure below also shows cable drops to several node devices and a

service access point.

If you are installing cables for a dual-cable network, the two cables should be

identified as cable A and cable B. Each of the cables should be routed using the

methods shown in the figure below.

A termination jumpers connected in each end tap

B termination jumpers removed from each inline tap

C drop cable

D trunk cable secured in raceway or conduit

E service access point

F strain reliefs

G node device

H end location

I inline location

J node device connector (part of drop cables)

K service loop

Note: The tapís internal termination jumpers are connected at the two end sites of

a cable section and disconnected and removed at each inline site on the cable

section (see p. 14).

shows a single-cable network cable run, or

each cable run (A or B) on a dual-cable network

A B

C

D

F

E

G

HI

I

KJ

H

G G


126 890 USE 100 00 November 2004

Route the cable between the site locations of the node device. Guidelines for cable

routing are described below. For dual-cable routing, follow these guidelines for each

cable.

! Use a continuous length of trunk cable between locations. Do not use any splices.

! In dual-cable installations, make sure that each trunk cable, tap, and drop cable

is properly marked so that it can be positively identified as belonging to cable A

or cable B over the entire end-to-end length of the network.

! At each tap location, allow sufficient trunk cable length for a service loop to

prevent pulling or twisting the cable.

! For each drop cable, provide a service loop to allow the connector to be

connected and disconnected at the network node device without any strain on the

cable. A service loop of 6 in (15 cm) minimum radius is adequate for most

installations.

! Install cable ties or clamps on each trunk cable segment as required for strain

reliefs to prevent the cable from pulling on the tap.

! Install cable ties or clamps on each drop cable as required for strain reliefs to

prevent the cable from pulling on the tap or node device connector.

! Use additional ties or clamps as required to secure each cable from flexing or

other damage in areas of mechanical motion devices and traffic.


890 USE 100 00 November 2004 127

Mounting the Taps

Overview Before mounting each tap, install the supplied grounding screw and nut into the tap

as shown in the figure below.

Before connecting any wiring to a tap, mount the tap at a location near its node

device panel. The tap must be near enough to the node device to allow the drop

cable to reach the node device with a service loop. See the figure below for an

example of the drop cable routing.

The location must also be accessible for installing the trunk and drop cables and for

future maintenance. The figure below shows the tapís outer and mounting

dimensions.

Install grounding screw and nutbefore mounting tap on panel

mountingcenters

3.16 in.(80.2 mm)

(56 mm)2.2 in

(122 mm)4.4 in

HoleDiam.

0.2 in.(5 mm)


128 890 USE 100 00 November 2004

Connecting the Trunk Cables

Cable Entry and

Jumpers (Taps at

Inline Sites)

At each inline site, two lengths of trunk cable will be installed. The cable to the right

side of the previous tap must connect to the left side of this tap. The cable to the left

side of the next tap must connect to the right side of this tap. The two jumpers must

be removed (see the figure below).

A network trunk cable

B right side of previous tap

C left side of next tap

D cable tie

E jumpers removed

A

B C

D

E

A

D


890 USE 100 00 November 2004 129

Cable Entry and Jumpers (Taps at

End Sites

At the two end sites on the cable section, one length of trunk cable will be installed.

It can be connected to either side of the tap. The two jumpers must be installed

between the center posts and the lower two posts at the side of the tap opposite from

the cable (see the figure below).

A Network trunk cable

B cable tie

C jumper installed

A

B

C

A

B

C


130 890 USE 100 00 November 2004

Connecting the Wires

Detailed instructions for making the connections are enclosed in each tap package.

Below is a general description of the connection. The terminal connections in the

graphic below are described in the following table.

The figure below shows how to connect each wire.

Graphic Legend Terminal Meaning Wire Color

A GND network bus, ground shield

B W network bus, white white

C Blk network bus, blue or black blue or black

D cable ties

Step Action

A Do not strip the wire. Place the wire into the terminal slot so that the end of the

wire is flush with the inside of the terminal.

B Using the proper insertion tool, press the wire into the terminal.

C Plastic caps are supplied with the tap. Press a plastic cap down fully into the

terminal.

A A

B B

C C

DD

topviewA B C


890 USE 100 00 November 2004 131

Connecting the Drop Cables

Connecting the Signal Wires

Detailed instructions for making the connections are enclosed in each tap package.

Below is a general description of the connections.

The drop cables contains two sets of twisted-pair signal wires with separate shield

wires. They also have an outer shield drain wire, for a total of seven wires.

! One set of wires is color-coded white and orange, with a bare shield wire.

! The other set is white and blue, with a bare shield wire.

Before connecting the wires, make sure you have identified the two sets of twisted-

pair wires. The two white wires are not interchangeable. When you connect the

wires, you must connect each wire to its proper terminal.

Insert the cable into the tap and secure it with a cable tie. Viewing the tap as shown

in the figure below, connect the wires. The terminals marked are described in the

following table

A O

B W

C GND

D BLU

E cable tie

F outer shield ground wire

Terminal Location Wire Color

O left orange

W left center white

GND center shields (both sets of wires)

W right center white

BLU right blue

A

B C BD

FE


132 890 USE 100 00 November 2004

The figure below shows how to connect each wire.

Connecting the Outer Shield

Wire

Install a ground lug on the outer shield drain wire. Tightly crimp or solder the lug to

the wire. Connect the lug to the tapís grounding screw as shown in the drop cable

connection figure above.

Step Action

A Do not strip the wire. Place the wire into the terminal slot so that the end of the

wire is flush with the inside of the terminal.

B Using the proper insertion tool, press the wire into the terminal.

C Plastic caps are supplied with the tap. Press a plastic cap down fully into the

terminal.

top

view

empty

terminal

BCA


890 USE 100 00 November 2004 133

Grounding

Overview At each tap, ensure that the drop cableís ground wire is connected to the tapís

grounding screw.

The tapís grounding path should be separate from paths used for motors,

generators, welders, and other high-current industrial devices. No other ground

wires (from other devices) should be connected to the tapís grounding screw.

At the node device end of the drop cable, the drop cableís ground wire must be

connected to the panel ground at the node site. This ground connection must be

made even if there is no node device connected to the drop cable connector at the

site.


134 890 USE 100 00 November 2004

Labeling

Overview After the cable is installed, label the cable segments for ease in future maintenance

of the network. Adhesive labels are available commercially for cable identification.

If a cable layout diagram exists for the installation, label each segment in

accordance with the diagram. If a diagram does not exist, refer to the examples

(see p. 47) and prepare a diagram showing the cable segments and method of

identifying them for future service. Then label the segments accordingly.

Affix the labels to the cables at each network node drop. Place them at a point that

will be visible to maintenance personnel.

Complete the network installation labeling by properly labeling each siteís cabinet or

enclosure, device mounting panel, and device.

Notify the person who will be responsible for future maintenance of the network, and

deliver the network documents to that person. It is suggested you do a walking tour

with that person through the network sites to produce familiarity with the network

layout.


890 USE 100 00 November 2004 135

Checking the Cable Installation

Overview This section describes how to visually inspect the cable and check its end-to-end

electrical continuity.

Inspecting the

Cable

Installation

Inspect and ensure the following.

! The cable runs should agree with the physical and electrical protection

requirements (see p. 48).

! The cable runs should agree with the network cable routing diagram (see p. 48).

! The tap at each of the two end drop sites on each section of the network should

have its two internal termination jumpers connected; they must be connected

between the two center posts and the W and B posts at the side of the tap

opposite from the trunk cable connection.

! The tap at each inline drop site should have its two internal termination jumpers

disconnected and removed.

! Service loops should exist on the trunk cable at each tap. Service loops should

exist on each drop cable at the node device end of the cable.

! Each tap should have the drop cableís ground wire connected to its grounding

screw; the drop cableís ground wire should also be connected to the panel

grounding point at the node device site.

! Adequate strain reliefs should be installed on the cable at each drop.

! All identification labels should be in place and properly marked.


136 890 USE 100 00 November 2004

Checking the Cable Continuity

Before checking continuity, disconnect all network cable connectors from the node

devices. Then

! Leave the drop cable ground lugs connected to their site panel grounds.

! At any node device connector, measure the resistance between pins 2 and 3 (the

signal pins). The resistance should be in the range 60 ... 80, which includes the

cable wire resistance.

! At each node device connector, check for an open circuit between pin 2 (a signal

pin) and pin 1 (the outer shield pin). Then check between pin 3 (a signal pin) and

pin 1. An open circuit should exist for both checks.

! At each node device connector, check the continuity between pin 1 (the outer

shield pin) and the plant ground point on the local site panel or frame. Direct

continuity should be present.

If your checks do not agree with these results, inspect the cable and all connections

for damage or miswiring and correct the condition.

The figure below shows the point-to-point wiring connections for a cable system with

two end sites and one inline site.

A end site tap

B inline site tap

C trunk cable

D drop cable

E tap ground

F panel ground

G drop cable connector

1

120

120

2 3 1 2 3 1 2 3

A B A

D

C E

F F F

G

890 USE 100 00 November 2004 137

6Connecting an RR85 Repeater

At a Glance

Overview This chapter discusses connecting an RR85 repeater.



Topic Page

Mounting Methods 138

Mounting Dimensions 139

Installing the Repeater 140

Reading the Network Indicators 143

RR85 Repeater Specifications 144

Connecting an RR85 Repeater

138 890 USE 100 00 November 2004

Mounting Methods

Overview As supplied, the RR85 repeaterís bottom surface is fitted with pads for mounting on

a horizontal surface, such as a shelf or platform. The unit is also supplied with

brackets for bolting it to a vertical panel.

The repeater is supplied with a power cable of 6 ft (2 m) length. You must provide

either 110 ... 120 VAC or 220 ... 240 VAC single-phase power. The power cable

connects to a socket on the rear panel. Grounding is supplied through the power

cable.

The repeater has a set of network indicators located on its top surface, near the front

of the unit. These indicate the communication status of the two links of the network

that are connected to the repeater. Your choice of mounting method should include

provision of access to the device for observing these indicators. You should also

locate the unit for easy access to its rear panel power and network cable connectors,

and for future servicing.

Horizontal Mounting

For mounting on a horizontal surface, place the unit at or below eye level to allow

viewing the network indicators. Secure it to the surface to prevent it from shifting its

position. Do not allow the unit to pull or strain on the network cables and power

cable.

The mounting brackets supplied with the unit for vertical panel mounting can also be

used to secure the unit on a horizontal surface.

Vertical

Mounting

For vertical mounting, use the brackets supplied with the unit for bolting to a panel.

The brackets have tabs that insert into slots provided on the repeaterís bottom

panel. No additional hardware is required for securing the brackets to the repeater.

You have to furnish hardware for bolting the repeater brackets to your panel. Four

bolts are required. Typically, standard 1/4-20 (10 mm) bolts or equivalent will be

satisfactory.

The repeaterís indicators will usually be readable at or slightly above eye level when

the unit is installed in the vertical position.


890 USE 100 00 November 2004 139

Mounting Dimensions

Overview Mounting dimensions for the repeater are shown in the figure below. The figure

shows the outer dimensions of the device, plus the total panel space required for the

device with its vertical mounting brackets installed.

MODICON

top view

rear panel view

Allow 4.0 in. (100 mm.) near clearance for cable and fuse access.

8.3 in.(211 mm.)

5.25 in.(133 mm.)

1.53 in.(39 mm)

2.59 in.(66 mm)

11.5 in (292 mm)

12.83 in (326 mm)14.08 in (358 mm)


140 890 USE 100 00 November 2004

Installing the Repeater

Overview

Mounting the

Repeater

Mount the repeater on the horizontal or vertical surface using the guidelines

described earlier in this chapter. Make sure you have proper access to he rear panel

connectors and power switch.

NETWORK INTERRUPTION

If you are replacing a repeater on an active Modbus Plus network, the

communication between the two links of the network will be temporarily disabled as

you disconnect the old device and connect the new one. The network signal path

passes through the repeater via its two rear panel connectors. This path will be

interrupted as you disconnect the cables from the ports.

Always plan for an orderly shutdown of your control process if necessary, while you

replace a repeater on an active network.


CAUTION


890 USE 100 00 November 2004 141

Connecting Power

The power cable supplied with the repeater is keyed for North American 110/120

VAC power outlets. If necessary, install a different plug on the cable for the power

source at your site.

Refer to the figure below. On the rear panel of the repeater, set the power selector

plug to the 110/120 VAC or 220/240 VAC position for the power source at your site.

To do this, remove the power selector plug by prying under its tab using a small

screwdriver. Set the plug to the proper voltage position as shown on the plug body,

then reinsert it.

A power selector plug and fuse

B power cable connector

C power switch

D Modbus Plus port 1 connector

E Modbus Plus port 2 connector

F power cable strain relief

Set the main power switch on the repeaterís rear panel to the 0 position (power off).

Plug the repeaterís power cable into the socket provided on the repeaterís rear

panel. Secure the power cable under the strain relief. Plug the cable into the power

source.

Using a continuity tester, verify the repeater chassis is grounded to the site ground.

Set the repeaterís main power switch to the 1 position (power on). The unitís power

OK indicator should illuminate.

A B C D E F


142 890 USE 100 00 November 2004

Connecting the Network Cables

Two sections of network trunk cable should already have been run to the repeater

site, representing the two links of the network that will be joined by the repeater.

Each set of cables should already have a network tap and a drop cable with

connector installed. If the cables and connectors are not in place, install them

correctly (see p. 121).

Each of the cable segments should be labeled to identify the link to which it

connects. If you are following a network layout diagram, it should show which cable

connector is to be mated to each repeater rear panel connector.

If the cable segments are not labeled or if you do not have a network layout diagram,

you can still connect the cables to the repeater and test your installation. The two

rear panel ports of the repeater operate identically. When you have connected the

cables, document your connection to facilitate future maintenance.

Refer to the above figure. Connect the two cable connectors to the repeaterís rear

panel connectors. If the network links are active, the unitís Modbus Plus port 1 and

Modbus Plus port 2 indicators should begin flashing.


890 USE 100 00 November 2004 143

Reading the Network Indicators

Overview The layout of the repeater indicators is shown in the figure below.

A Modbus Plus

B power

C port 2

D port 1

E OK

The power ok indicator illuminates steadily when the repeater has normal power

from the AC line and its internal power supply is operating normally.

The repeater has two indicators that show the communication status at its two

Modbus Plus ports. Each portís indicator flashes when a transmission occurs at the

port.

The intensity of each port indicator reflects the relative rate of transmission at the

port. As the indicator illuminates during transmission, this in turn reflects the relative

amount of network activity received at the opposite port. For example, if the port 2

indicator is brightly illuminated, indicating that this port is highly active, it shows that

a high level of activity is being received from the network section at port 1.

If a port indicator fails to illuminate, or is illuminated only dimly, it can indicate a very

low level of activity on the opposite portís cable.

C

A A B

D E


144 890 USE 100 00 November 2004

RR85 Repeater Specifications

Overview

Description Name RR85 Modbus Plus network repeater

Part Number NW-RR85-000

Physical

Characteristics

Height 2.59 in (66 mm)

Width 11.5 in (292 mm), unity only 14.08 in (358 mm),

with mounting brackets

Depth 8.30 in (211 mm)

Weight 5.5 lbs (2.5 kg) net

6.5 lbs (3.0 kg) shipping

Power Requirements 115/230 VAC + 15%

47 ... 63 Hz, 10 W

Access rear panel power connector with on/off switch

Fuse 1.0 A, 3 AG SB

Environmental Temperature 0 ... 60 degrees C, operating

-40 ... +80 degrees C, storage

Humidity 0 ... 95%, non-condensing

Altitude 10,000 ft (3 km), maximum

EMI, Radiated

Susceptibility

MIL STD 461B RS03

EMI, Conducted

Susceptibility

MIL STD 461B CS03

Network

Connections

Rear Panel Connectors mate with Modbus Plus drop cables

890 USE 100 00 November 2004 145

7Connecting a BP85 Bridge Plus

at a Glance

Overview This chapter discusses connecting a BP85 bridge plus.



Topic Page

Mounting Methods 146

Dimensions (Panel/Shelf Models) 147

Dimensions (Rack Mount Model) 148

Setting the Modbus Plus Addresses 149

Connecting the Power Cables 150

Connecting the Network Cables 152

Applying Power 153

Reading the Network Indicators 154

Attaching Port Identification Labels 156

BP85 Bridge Plus Specifications 157

Connecting a BP85 Bridge Plus

146 890 USE 100 00 November 2004

Mounting Methods

Overview BP85 models are available for mounting on a horizontal shelf or vertical panel, or for

installation into a standard 19-inch rack.

Your choice of a mounting method should provide access for observing the front

panel indicators. You should also provide access to the unitís rear panel for setting

the switches, connecting the cables, and servicing.

Horizontal or

Vertical

Mounting

Models for horizontal or vertical mounting are fitted with pads on their bottom

surface, and are supplied with mounting brackets. The brackets can be used to

secure the unit to the horizontal shelf or vertical panel.

No additional hardware is needed for attaching the brackets to the BP85. You will

have to furnish hardware for bolting the brackets to your panel or shelf. Four bolts

are required. Typically, standard 1/4-20 (10 mm) bolts or equivalent will be

satisfactory.

Rack Mounting Rack-mount models are designed for installation into a standard 19-inch rack. You

must furnish the hardware for bolting the unit to your rack. Four bolts are required.

The BP85 unit can support itself in the rack by its front mounting bolts. It is light

enough that you do not have to provide rear support within the rack.

Bridge Plus Models

Part Number Mounting Method Operating Power

(Nominal)

Modbus Plus

Network Cable

NW-BP85-000 panel or shelf 115/230 Vac or 24 Vdc single

NW-BP85-002 panel or shelf 115/230 Vac or 24 Vdc single or dual

NW-BP85D002 19-inch rack 125 Vdc or 24 Vdc single or dual


890 USE 100 00 November 2004 147

Dimensions (Panel/Shelf Models)

Overview BP85 bridge plus dimensions (panel/shelf models)

MODICON

top view

rear panel view

allow 4.0 in. (100 mm.) rear clearance for access to

8.3 in.(211 mm) 5.25 in.

(133 mm)

1.53 in.(39 mm)

2.59 in.(66 mm)

11.5 in (292 mm)

12.83 in (326 mm)

14.08 in (358 mm)

switches, cables, and fuse

ModbusBridge PlusNW-BP85-000


148 890 USE 100 00 November 2004

Dimensions (Rack Mount Model)

Overview BP85 bridge plus dimensions (rack mount model)

MODICON

front panel view

top view

3.0(7.6 mm)

3.47(88 mm)

18.25 in (464 mm)

19.0 in (483 mm)

17.25 in (438 mm)

allow 4.0 in (100 mm) rearclearance for

access toswitches, cables,

and fuse

8.48 in(215 mm)

1.44(37 mm)

9.15 in(232 mm)

10.59 in(269 mm)


890 USE 100 00 November 2004 149

Setting the Modbus Plus Addresses

Overview Before you apply power to the BP85, you must set the unitís network addresses in

two groups of switches on the unitís rear panel.

Because the BP85 serves two networks, it has a set of port connectors for each

network and an associated group of switches for assigning the unitís addresses on

each network. The figure below shows the switch locations, switch setup

combinations, and resulting addresses.

Set each group of switches to the BP85ís address on the network that will be

connected to the port connector. The network address will be one higher than the

binary value you set into switches 1 ... 6. Switches 7 and 8 are not used.

Below are examples of the BP85 network address switch settings.

port 2 addressupper switches

port 1 addresslower switches

BP85-002

port 1 address left switches

port 2 addressright switches

BP85-0001 2 3 4 5 6 7 8

0 position = down

Addresses 1 2 3 4 5 6 7 8

1234567891011121314151617181920212223242526272829303132

0 0 0 0 0 0 - -1 0 0 0 0 0 - -

0 1 0 0 0 0 - -1 1 0 0 0 0 - -0 0 1 0 0 0 - -1 0 1 0 0 0 - - 0 1 1 0 0 0 - -

1 1 1 0 0 0 - -0 0 0 1 0 0 - -1 0 0 1 0 0 - -0 1 0 1 0 0 - -1 1 0 1 0 0 - -0 0 1 1 0 0 - -1 0 1 1 0 0 - -0 1 1 1 0 0 - -1 1 1 1 0 0 - -0 0 0 0 1 0 - -1 0 0 0 1 0 - -0 1 0 0 1 0 - -1 1 0 0 1 0 - -0 0 1 0 1 0 - -1 0 1 0 1 0 - -0 1 1 0 1 0 - - 1 1 1 0 1 0 - -0 0 0 1 1 0 - -1 0 0 1 1 0 - -0 1 0 1 1 0 - -1 1 0 1 1 0 - -0 0 1 1 1 0 - -1 0 1 1 1 0 - -0 1 1 1 1 0 - -1 1 1 1 1 0 - -

Addresses 1 2 3 4 5 6 7 8

3334353637383940414243444546474849505152535455565758596061626364

0 0 0 0 0 1 - -1 0 0 0 0 1 - -0 1 0 0 0 1 - -1 1 0 0 0 1 - -0 0 1 0 0 1 - -1 0 1 0 0 1 - -0 1 1 0 0 1 - -1 1 1 0 0 1 - -0 0 0 1 0 1 - -1 0 0 1 0 1 - -0 1 0 1 0 1 - -1 1 0 1 0 1 - -0 0 1 1 0 1 - - 1 0 1 1 0 1 - -0 1 1 1 0 1 - -1 1 1 1 0 1 - -0 0 0 0 1 1 - -1 0 0 0 1 1 - -0 1 0 0 1 1 - -1 1 0 0 1 1 - -0 0 1 0 1 1 - -1 0 1 0 1 1 - -0 1 1 0 1 1 - -1 1 1 0 1 1 - -0 0 0 1 1 1 - -1 0 0 1 1 1 - -0 1 0 1 1 1 - -1 1 0 1 1 1 - -0 0 1 1 1 1 - -1 0 1 1 1 1 - -0 1 1 1 1 1 - -1 1 1 1 1 1 - -

switch position switch position


150 890 USE 100 00 November 2004

Connecting the Power Cables

Overview

AC/DC Models AC/DC models are supplied with a power cable of 6 ft (2 m) length for operation from

110-120 Vac or 220 -240 Vac single-phase power. The cable connects to a socket

on the rear panel. Grounding is though the cable. The AC line switch is located on

the rear panel. The unit contains an AC line fuse that is accessible on the rear panel.

These models can also operate from an external 24 Vdc source. Power connects to

a socket on the rear panel. Grounding is through the cable. The DC source must be

switched and fused externally to the unit.

DC/DC Models DC/DC models operate from a 125 Vdc or 24 Vdc source. Power connects to a

terminal strip on the rear panel. A grounding terminal is provided. The DC source

must be switched and fused externally to the unit.

Connecting AC

Power

Set the BP85 power switch to the "0" (power off) position. Connect the BP85 to the

power source. Test the connection by setting the power switch to ë1í (power on). The

power indictor should illuminate.

Before connecting the network cables, set the power switch to the ë0í (power off)

position. The power indicator should not be lit.

Connecting DC

Power

Set the external DC power source to off. Connect the BP85 to the source. Test the

connection by setting the DC power source to on. The power indicator should

illuminate.

Before proceeding with the connection of the network cables, set the DC power

source to off. The power indicator should not be lit.

POSSIBLE NETWORK INTERRUPTION

If you are replacing a bridge plus on an active network, the communication between

the networks served by the bridge plus will be temporarily disabled as you

disconnect the old device and connect the new one. Always plan for an orderly

shutdown of your control process, if necessary, while you replace a bridge plus on

an active network.


CAUTION


890 USE 100 00 November 2004 151

Before You Apply Power

Do not apply power to the BP85 until you have completed the setup of the unitís

network address switches for both networks. The settings will be sensed by the unit

when power is applied. The figure below is an example of a BP85 bridge plus

connector.

rear panel view

BP85-000power cable strain relief

MB+ port 1 MB+ port 2 (right) MB+ port 2 address switches

(left) MB+ port 1 address switches

AC power switch

AC power connector

AC power selector plug and fuse

BP85-002MB+ port 1

B

MB+ port 2B

power cablestrain relief

(upper) MB+ port 2 address switches

(lower) MB+ port 1 address switchesMB+ port 1

AMB+ port 2

A

AC power switch

+ -24 VDCAC power connector

AC power selectorplug and fuse

BP85D002MB+ port 1

BMB+ port 2

BGND

MB+ port 1A

MB+ port 2A

(upper) MB+ port 2 address switches

(lower) MB+ port 1 address switches

+ - + -125 VDC 24 VDC


152 890 USE 100 00 November 2004

Connecting the Network Cables

Overview If the cables and connectors are not in place, install them correctly (see p. 121). If

the network cables are not labeled, contact the person who is responsible for the

network planning and layout before proceeding. When you have this information,

connect the cables as described below.

Connect the network cable connectors to the connectors provided on the bridge

plusís rear panel. If the networks are active, the unitís Modbus Plus port 1 and

Modbus Plus port 2 indicators should begin flashing.

! Connecting single-cable units on single-cable networks:If you are installing a single-cable unit (BP85-000) on networks that have a single

cable, you will have two cables to connect to your BP85. Connect the cables to

the port 1 and port 2 connectors. Secure each connector by tightening its two

screws.

! Connecting dual-cable units on dual-cable networks:

If you are installing a dual-cable unit (BP85-002) on a dual-cable network, you will

have four cables to connect to your BP85. Each network should have two cables,

labeled A and B. Connect the cables to the connectors on the BP85 rear panel.

secure each connector by tightening its two screws.

! Connecting dual-cable units on single-cable networks:

If you are installing a dual-cable unit (BP85-002) on networks that have a single

cable, you will have two cables to connect to your BP85. Connect the cables to

the port 1 A and port 2 A connectors. Plug two terminating connectors (AS-

MBKT-185) into the port 1 B and port 2 B connectors. Secure each connector by

tightening its two screws.


If the network cables are not labeled, or if you do not have a layout diagram

showing which cable is to be connected to each connector on the bridge plus, you

should not connect the cables until you obtain this information. The bridge pus

connectors have dedicated network addresses that you have set in the unitís

address switches. Incorrect connection of he cables can cause a disruption of

communication on the networks.


CAUTION


890 USE 100 00 November 2004 153

Applying Power

Overview After you have set the address switches to the desired network addresses and

connected the network cables, you can apply main power to he BP85.

AC Power If you are using AC power, set the power switch on the BP85 rear panel to the 1

position (power on).

DC Power If you are using DC power, switch it on from its external source.

The BP85ís power OK indicator should illuminate. When the unit completes its

internal diagnostic tests, the ready indicator should illuminate.


154 890 USE 100 00 November 2004

Reading the Network Indicators

Overview The layout of the bridge plus indicators is shown in the figure below.

Power OK illuminates when the BP85 has normal power from the source. Ready

(NW-BP85-000 only) illuminates when the BP85 has successfully completed its

internal diagnostics.

Error chan A and error chan B show the fault status on the two cable paths for each

network. If an indicator blinks momentarily, it indicates that a message error was

detected on the path. a steady on state indicates a hard fault either in the cable or

in a node device connected to the cable.

Port 1 and port 2 show the communication status at the two Modbus Plus network

ports. status is shown by flashing a repetitive pattern. The patterns are:

! Six flashes: This is the bridge plusís normal operating state. All nodes on the

network should be flashing this pattern. If a port indicator is off continuously, the

bridge plus is not transmitting at that port.

! One flash The bridge plus node is offline after just being powered up, or after

hearing a message from another node with the same network address (duplicate

addresses are not allowed). In this state, the node monitors the network and

builds a table of active nodes and token-holding nodes. It remains in this state for

five seconds, then attempts to go to its normal operating state.

BP85-000

BP85-002

BP8D002

Modbus

Plus

port 2

Modbus

Plus

port 1

power

ok

ready

power

ok

MP

port 1error

chan B

error

chan A

MP

port 2

error

chan B

error

chan A

error

chan A

error

chan B

MP

port 2

error

chan A

error

chan B

MP

port 1

power

ok


890 USE 100 00 November 2004 155

! Two flashes, then off for 2 s: The bridge plus node is hearing the token being

passed among other nodes, but is never receiving the token. Check the network

link for an open or short circuit, or defective termination.

! Three flashes, then off for 1.7 s: The bridge plus node is not hearing any other

nodes. It is periodically claiming the token, but finding no other node to which to

pass it. Check the network link for an open or short circuit, or defective

termination.

! Four flashes, then off for 1.4 s: The bridge plus node has heard a valid

message from another node that is using the same address as this node. The

node remains offline in this state as long as it continues to hear the duplicate

address. If the duplicate address is not heard for five seconds, the node then

changes to the pattern of one flash every second.


156 890 USE 100 00 November 2004

Attaching Port Identification Labels

Overview Two sets of Modbus Plus port labels are supplied with your bridge plus. Each set

contains two labels. One set is used to identify the Modbus Plus networks and node

addresses at the deviceís port connectors. The other set is a spare.

The labels are designed to provide ready information to persons who will maintain

the network in the future. Enter the Modbus Plus network numbers and network

addresses you have assigned to the Bridge Plus. Place the labels on the unit so that

they can readily identify the network and node address at each port connector.

Example:

Modbus Plus Modbus Plus

1

23

2

22Node Node


890 USE 100 00 November 2004 157

BP85 Bridge Plus Specifications

Overview BP85 bridge plus specifications (panel/shelf model)

Description Name BP85 Modbus Plus network bridge

Part Number NW-BP85-000 (single cable)

Physical

Characteristics


Width 11.5 in (292 mm), unit only 14.08 in

(358 mm), with mounting brackets




AC Power Requirements 115/230 VAC + 15%

47 ... 63 Hz, 10 W

Access rear panel power connector with on/

off switch

Fuse 1.0 A, 2 AG SB

DC Power (NW-

BP85-002 only)

Requirements 24 VDC + 15%

Access rear panel power connector,

requires external on/off switch

Fuse requires external 1.0 A fast-blow

fuse

Environmental Temperature 0 ... 60 degree C, operating




EMI, Radiated Susceptibility MIL STD 461B RS03

EMI, Conducted Susceptibility MIL STD 461B CS03

Network

Connections



158 890 USE 100 00 November 2004

BP85 bridge plus specifications (rack mount model)

Description Name BP85 Modbus Plus network bridge

Part Number NW-BP85D002 (dual cable)

Physical

Characteristics


Width 19.0 in (483 mm)




DC Power Requirements 105 ... 140 VDC or 24 VDC + 15%

Ground Leakage 1 mA @ 140 VDC

Input Current 41 mA @ 125 VDC

Inrush Current 6 A @ 125 VDC typical

Access rear panel terminal strip, requires

external on/off switch

Fuse 24 VDC: requires external 1.0 A

fast-blow fuse

125 VDC: requires external 2.0 A

slow-blow fuse

Environmental Temperature 0 ... 60 degrees C, operating




EMI, Radiated Susceptibility IEC 801-3, level 3

Surge Withstand, Fast Transient IEC 801-4, level 3

Surge Withstand, Oscillatory Wave IEEE 472

Surge Transients IEEE 801-5, level 3

Electrostatic Discharge IEEE 801-2, level 3

Reliability Service Life 5 years

MTBF 50,000 hours maximum @ 30

degrees C, assuming fixed ground

and component stress with

maximum specifications

Network

Connections


890 USE 100 00 November 2004 159

Appendices

At a Glance

Overview This chapter discusses the following topics.

! Modbus Plus transaction elements

! message routing

! planning worksheets

! installing custom cable systems

What's in this

Appendix?

The appendix contains the following chapters:

Chapter Chapter Name Page

A Modbus Plus Transaction Elements 161

B Message Routing 171

C Planning Worksheets 183

D Installing Custom Cable Systems 195

Appendices

160 890 USE 100 00 November 2004

890 USE 100 00 November 2004 161

AModbus Plus Transaction Elements

At a Glance

Overview This appendix discusses Modbus Plus transaction elements.



Topic Page

Transaction Timing Elements 162

The Message Format HDLC Level 166

The Message Format MAC Level 167

The Message Format LLC Level 168

Modbus Plus Transaction Elements

162 890 USE 100 00 November 2004

Transaction Timing Elements

Token Holding Time

Each node holds the network token for a minimum length of time if it has no

transactions. The minimum token time is approximately 530 microseconds. The

token will be held for a longer time depending upon the quantity and size of pending

transactions.

Typical times are shown in the charts below. Each chart shows the types of

transactions the device can handle, how many concurrent transactions are

available, and the times required to process single and multiple paths. Times are

shown for small and large size transactions. All times are in milliseconds.

Worst Case

Timing Examples

controllers

Note: The token holding times shown in the right column are worst-case times, with

all of the deviceís paths active, with all paths moving the full amount of data, and

with full queueing. With proper network design, these times should not occur in

practice.

The only types of transactions that you should consider for calculating the loading

on a properly-designed network are the data master paths and data slave paths,

with occasional queueing.

You should plan your network and application programming to avoid the worst-

case times. Use the formulas (see p. 75) to predict response times under various

loading conditions. See the guidelines (see p. 63) for designing your network to

avoid or minimize queuing in your application.

Two Registers 100 Registers

Transaction

Type

Available

Transactions

One

Transactio

n

All

Transactions

One

Transaction

All

Transaction

s

MSTR DM

path

4 1.4 5.6 3.0 12.0

DS path 4 1.4 5.6 3.0 12.0

Dequeue

transaction to

slave path

4 1.4 5.6 3.0 12.0

PM path 1 1.4 1.4 3.0 3.0

PS path 1 1.4 1.4 3.0 3.0

Totals 8.4 21.0 18.0 45.0


890 USE 100 00 November 2004 163

SA85 and SM85 network adapters

BP85 bridge plus devices


Transaction

Type

Available

Transactions

One

Transaction

All

Transaction

s

One

Transaction

All

Transaction

s

DM path 8 1.4 11.2 3.4 27.2

DS path 8 1.4 11.2 3.4 27.2

dequeue

transaction to

slave path

8 1.4 11.2 3.4 27.2

PM path 8 1.4 11.2 3.4 27.2

PS path 8 1.4 11.2 3.4 27.2

Totals 7.0 56.0 17.0 136.0


Transaction

Type

Available

Transactions

One

Transactio

n

All

Transactions

One

Transaction

All

Transaction

s

DM path 8 1.4 11.2 3.4 27.2

DS path 8 1.4 11.2 3.4 27.2

dequeue

transaction to

slave path

8 1.4 11.2 3.4 27.2

PM path 8 1.4 11.2 3.4 27.2

PS path 8 1.4 11.2 3.4 27.2

Totals 7.0 56.0 17.0 136.0


164 890 USE 100 00 November 2004

BM85 bridge multiplexers

Data Response

Time

When a nodeís application program initiates a transaction, the time required for a

data response to be returned to the application depends upon several factors:

! the internal timing of the initiating node

! the token rotation and transmission timing on the network

! the internal timing of the responding node

The figure below illustrates the elements of one read or write transaction as it occurs

in initiating and responding controller nodes. The transaction is moving 100 registers

of data. Where the times differ between operations, the read transaction timing is

shown with an (R) and the write timing with a (W).

Timing starts when an MSTR is enabled in the initiating node. The transaction is

finished when the MSTR functionís complete output is on. In the case of the read,

registers will be updated in the initiating node at that time.

The token rotation time of the network and the scan times of the devices will usually

predominate in the end-to-end timing of the transaction. The other timing elements

are typically much shorter than the token rotation and scan times. See p. 55 to

predict response times and throughput in your network design.


Transaction

Type

Available

Transactions

One

Transactio

n

All

Transactions

One

Transaction

All

Transaction

s

MSTR DM

path

4 1.4 5.6 3.0 12.0

DS path 4 1.4 5.6 3.0 12.0

dequeue

transaction to

slave path

4 1.4 5.6 3.0 12.0

PM path 4 1.4 5.6 3.0 12.0

PS path 4 1.4 5.6 3.0 12.0

Totals 7.0 28 15.0 12.0


890 USE 100 00 November 2004 165

The figure below represents the timing elements of a read or write transaction

initiating node

responding node

0.5 -1.50.2 (R)

1.8 (W)0.3

1.8 (R)

0.2 (W)0.3 0.5 -1.5

0.2 (R)

1.8 (W)0.3

0.5 -1.5 0.5 0.5 -1.51.8 (R)

0.2 (W)0.3

receive send 0 to 1

tramsfer command

host

transfer command

0 ... 1send receive

transfer

command

to

peer

processor

0 ... 1

token

rotation

transfer

command

to

host

processor

receive

response

send

Rckrec

Rck

send

command0 to 2

scans

to host processor

processingcommand Rck scan

to peer processor

tokenrotation

response Rck

Note: ! Transaction example is for Modicon programmable controllers.

! Data length is 100 registers.

! All timing is in milliseconds.

! All timing is approximate (not to scale).

! (R) = read; (W) = write


166 890 USE 100 00 November 2004

The Message Format HDLC Level

Overview Messages appearing on the network contain three levels of protocol to handle the

process of synchronization, routing, transferring data, and checking for errors. The

message format satisfies the network HDLC, MAC, and LLC level protocols.

The figure below illustrates the high-level data link control (HDLC) level format of a

typical message transmitted from a networked controller. The format at the other

levels is shown on the following pages.

HDLC Fields At the HDLC level, the network protocol defines the beginning and end of the

message frame, and appends a frame check sequence for error checking. The

message contains the following HDLC level fields:

preamble

AA

opening

flag

7E

BDCST

address

FF

MAC/LLC field FCS

CRC-16

closing

flag

7E

Length: 1 1 1 2 1

HDLC Level

Field

Description

Preamble One byte, OxAA (hexadecimal AA or alternating ones and zeros).

Opening Flag One byte, Ox7E (one zero, six ones, one zero).

Broadcast

Address

One byte, OxFF (eight ones). These contents specify that all nodes receive

the frame. Each node will then parse the frameís MAC level contents to

recognize its address as the intended destination.

MAC/LLC

Data

This field specifies the MAC level control packet for token-related operations

and contains both the MAC and LLC level packets for data-message related

operations.

If the message relates to the token-passing operation of the network, the

field contains only the MAC level information necessary to identify a

successor. If the message contains data, the field contains both MAC and

LLC level information.

The MAC and LLC level packets are detailed on the following pages.

Frame Check

Sequence

Two bytes containing the CRC 16 frame error check sum.

Closing Flag One byte, Ox7E (one zero, six ones, one zero).


890 USE 100 00 November 2004 167

The Message Format MAC Level

Overview At the medium access control (MAC) level, the network protocol defines the

message destination and source nodes, and controls the passing of tokens.

The figure below illustrates the MAC level format of a message containing a Modbus

command. The Modbus command is imbedded in the LLC field of the frame.

MAC Fields The message contains the following MAC level fields:

length:

preamble

AA

opening

flag

7E

BDCST

address

FF

MAC/LLC fieldFCS

CRC-16

closing

flag

7E

dest

address

source

addressMAC

function

byte

countLLC field (includes Modbus command)

1 1 1 2 1

Mac Level

Field

Description

Destination

Address

The address of the node intended to receive the message, in the range of 1

to 64. Additional information identifying the message transaction in the

nodeís application is contained in the LLC level packet.

Source

Address

The address of the node originating the message, in the range of 1 to 64.

MAC Function

Code

This field defines the action to be performed at the MAC level by the

destination.

Byte Count This field defines the quantity of data byte to follow in the message.

LLC Data This field contains the LLC level packet, which includes the Modbus

command. The LLC field is detailed on the next page.


168 890 USE 100 00 November 2004

The Message Format LLC Level

Overview At the logical link control (LLC) level, the message contains the data field to be

transferred, such as the Modbus command. It also contains additional routing and

message control fields.

The figure below illustrates the LLC level format of a message containing a Modbus

command.

HDLC level:

preamble

AA

opening

flag

7E

BDCST

address

FF

MAC/LLC fieldFCS

CRC-16

closing

flag

7E

Length:

Length:

dest

address

source

addressMAC

function

byte

countLLC field

Master

output

path

router

counter

trans

sequence

number

routing path Modbus frame (modified)

Length:

MAC level:

LLC level:

1 1 1 2 1

1 1 1 2

1 1 1 5


890 USE 100 00 November 2004 169

LLC Fields The message contains the following LLC level fields:

LLC Level

Field

Description

Master Output

Path

One byte identifying the originating nodeís output path for transmission of

the message. Although each controller has one physical port for access to

the network, it maintains multiple transactions to remain queued within the

controller while it completes communications with other controllers. The

controller will reserve the specified path until its transactions on that path

are completed.

Router Counter This field counts the number of bridge plus devices traversed to control

message queueing. Messages are queued in the first bridge only.

Transaction

Sequence

One byte identifying the transaction between the source and destination.

Multiple messages associated with a single transaction contain a value that

remains constant while the transaction is active.

If a source initiates a message requesting data from a destination, the

returned data message will include the same transaction sequence value.

If the source initiates a message requesting data from a destination and

then aborts the transaction before receiving the data, the source can initiate

a new message with the same destination without waiting for returned data

for the aborted transaction. The two messages will have different

transaction sequence values. When returned data is received from the

destination, the transaction sequence value in the received message will

identify the data as being either from the aborted transaction or from the

newly initiated one.


170 890 USE 100 00 November 2004

Routing Path For messages to programmable

controller nodes on Modbus Plus:

Each non-zero byte, except the last,

specifies routing through a bridge

plus to another network. The last

non-zero byte specifies the

destination controllerís node

address (1-64).

For messages to SA85 host based

device nodes:

Each byte, up to and including the

deviceís node address, specifies

routing to the device. Bytes following

the node address byte can be used

by the host application to specify

application tasks running in the host.

For messages to a single Modbus

slave device connected to a bridge

multiplexer port:

Each non-zero byte, except the last

two, specifies routing through a

bridge plus to another network. The

last two non-zero bytes specify the

bridge multiplexerís node address

(1-64) and Modbus port (1-4)

respectively.

For messages to a Modbus

networked slave device connected

to a bridge multiplexer port:

Each non-zero byte, except the last

three, specifies routing through a

bridge plus to another network. The

last three non-zero bytes specify the

bridge multiplexerís node address

(1-64), Modbus port (1-4), and slave

address (1-247) respectively.

Modbus Frame

(modified)

This field contains the Modbus command originated by the controller or a

Modbus master device connected to the controller. Data in a Modbus

response message would also be contained in this field.

The field contents are the same as the original Modbus message, with two

exceptions:

! The Modbus slave address is stripped from the contents. It appears in

the Modbus Plus MAC level destination field.

! The Modbus CRC/LRC error check is stripped from the contents. Error

checking is performed on the entire message in the Modbus Plus HDLC

level CRC − 16 field.

LLC Level

Field

Description

890 USE 100 00 November 2004 171

BMessage Routing

At a Glance

Overview This appendix discusses message routing.



Topic Page

The Modbus Plus Message Routing Path 172

Modbus Address Conversion 174

Controller Bridge Mode Routing 175

Bridge Multiplexer Routing 177

Message Routing

172 890 USE 100 00 November 2004

The Modbus Plus Message Routing Path

Overview A single Modbus Plus network can have up to 64 addressable node devices, with

each device having a unique address of between 1 and 64. Multiple networks can

be joined through bridge plus devices. Devices address each other across bridge

plus devices by specifying routing paths of five bytes, with each byte representing

an address on the next network. This routing method allows nodes in other networks

to be addressed up to four networks away from the originating node.

The routing path is imbedded in the Modbus Plus message frame as it is sent from

the originating node.

The figure above illustrates message routing to a programmable controller through

three networks that are joined by bridge plus nodes. Using the routing addresses in

the figure, the message will first be routed to node 25, a bridge plus on the local

network. That node forwards the message on to the bridge plus at address 20 on the

second network. The second bridge plus forwards the message to its final

destination, node address 12 on the third network. The zero contents of bytes 4 and

5 specify that no further routing is needed.

Programmable

Controllers

For programmable controllers, the last non-zero byte in the message routing

specifies the network node address of the controller (1 to 64).

Host-Based

Network

Adapters

For host-based network adapters, the routing bytes specify the networkís route to

the adapterís node address. Any bytes following the adapterís address can be used

internally by the adapter application program (for example, to route messages to

specific tasks within the application). Routing details are provided in the guidebook

for each host-based device.

Modbus Plus

message frame

Example:

Routing address 2 = 20


Routing addresses 4 and 5

are zero (no further routing).

routing

path

routing address 1routing address 2

routing address 3

routing address 4routing address 5

start end


Message Routing

890 USE 100 00 November 2004 173

Bridge Multiplexers

For bridge multiplexers, the routing field contents are specific to the type of device

being addressed.

For a single slave device at a Modbus port, two bytes are used to address the

device. The next-to-last non-zero byte addresses the multiplexer node (1 to 64). The

last non-zero byte specifies the port (1 to 4), and therefore the single device.

For a networked Modbus slave device, three bytes are used to address the device.

The third byte from the last non-zero byte addresses the multiplexer node (1 to 64).

The next-to-last non-zero byte specifies the Modbus port (1 to 4). The last non-zero

byte specifies the Modbus address of the slave device (1 to 247).

Message Routing

174 890 USE 100 00 November 2004

Modbus Address Conversion

Overview Modbus devices use addresses of one byte in the range 1 ... 255. Modbus Plus

nodes are addressed in the range 1 ... 64, with five bytes of routing imbedded in

each Modbus Plus message.

Modbus messages received at the Modbus port of a programmable controller in

bridge mode must be converted to the five-byte routing path used on Modbus Plus.

Modbus messages received at a bridge multiplexer Modbus port must also be

converted.

The Modbus address in the message determines the final routing over Modbus Plus.

The figure below compares the methods used by programmable controllers in bridge

mode and bridge multiplexers for converting modbus addresses.

Programmable controllers convert the address using the methods shown in the

figure below. Bridge multiplexers first compare the address to an internal table of

Modbus Plus paths, using routing from the table if a match is found. If a match is not

found in the table, the methods shown in the figure below are used.

Note: The addressing methods for both devices are identical except for addresses

in the range 70 ... 79. Addressing is described in detail on the following pages.

256 255

80

79

70

69

65

64

1

0

80

79

75

74

71

70 65

64

1

0

implicit

attach

address

implicit

attach

address

explicit

attach

address

direct

attach

address

reserved

reserved

reserved

reserved

reserved

direct

attach

address

programmable

controller

bridge

multiplexer

Message Routing

890 USE 100 00 November 2004 175

Controller Bridge Mode Routing

Overview If a Modbus message is received at the Modbus port of a controller that is set to

bridge mode, the address (in the range 1 ... 255) is converted as shown in the figure

below.

Address Range 1 ... 64

If the address is in the range 1 ... 64 (direct attach address), the message is routed

to the specific node address 1 ... 64 on the local Modbus Plus network.

255

80

79

70

69

65

64

1

0

implicit

attach

address

explicit

attach

address

reserved

reserved

direct

attach

address

Message Routing

176 890 USE 100 00 November 2004


If the address is in the range 70 ... 79 (explicit attach address), it causes the

controller to access an address map table stored in a set of holding (4x) registers.

These registers are located immediately following the free-running timer register in

user logic (you must therefore implement the timer in your logic program). Modbus

addresses in this range thus become pointers to the routing table, which contains 10

stored routing paths for Modbus Plus.

The routing path pointed to by the Modbus address is applied to the message. Each

path is five bytes in length.

Address Range

80 ... 255

If the address is in the range 80 ... 255 (implicit attach address), it will be divided by

10. The quotient and remainder of the division will become the first two bytes of the

five byte routing path. The remaining three bytes of the routing path will always be

zeros. This addressing method allows two levels of addressing across Modbus Plus

networks.

4x Free-Running Time

70 4x+ 1 routing path 1, byte 1

4x+ 2 routing path 1, byte 2




71 4x+ 6 routing path 2, byte 1

. . . . . .


Message Routing

890 USE 100 00 November 2004 177

Bridge Multiplexer Routing

Modbus Address Map

If a Modbus message is received at a BM85 Modbus port, the address (1 ... 255) is

compared to an internal Modbus address map table for the port. The map table

contains up to 64 addresses, each pointing to a five-byte routing path. If an address

match is found in the table, the routing path is applied to the message. If the first byte

is in the range 1 ... 64, the message is routed out on Modbus Plus. If the first byte is

zero, the message goes to a Modbus port (1 ... 4) specified in byte two. If that port

has a single slave device, the remaining three routing bytes should be zeros. If the

port has a network of slave devices, byte three is the slave address.

If a match is not found in the table, address conversion proceeds as in the figure

below.


If the address is in the range 1 ... 64 (direct attach address), the message is routed

to the specific node address 1 ... 64 on the local Modbus Plus network.

Address Range

71 ... 74

If the address is in the range 71 ... 74 (MUX attach address), the message is routed

to a single Modbus device at one of the bridge multiplexerís Modbus ports.

Addresses 71 ... 74 specify ports 1 ... 4 respectively.

255

implicit

attach address

reserved

reserved

reserved

MUX attach

address

direct

attach

address

Note:

Addresses 65 ... 79 are all

reserved for BM85 ports

that are configured in the

silent master mode.

80

79

75

74

71

70

65

64

1

0

Message Routing

178 890 USE 100 00 November 2004


If the address is in the range 80 ... 255 (implicit attach address), it will be divided by

10. The quotient and remainder of the division will become the first two bytes of the

five byte routing path. The remaining three bytes will always be zeros. This

addressing method allows two levels of addressing across Modbus Plus networks.

Silent Master

Ports

A BM85 serial port can be configured as a silent master port. A network with one

master and a set of slave devices can be connected to the port. The master can

initiate communication with a local slave device or across Modbus Plus. The slave

device addresses must be unique. They must not be the same as a node address

(1 ... 64) on the BM85ís local network, and they must not exist as entries in the

mapping table for the port. Addresses 65 ... 79 are reserved.

Message Routing

890 USE 100 00 November 2004 179

Routing Examples

The figure below illustrates message routing across two networks.

Note: Standby unit assumes primary address plus 32.

M

M

M

M

M

M

M

master

C

CPU C

master

A

slave

A

network

slave 50

network

slave 100

network

slave 150

network

slave 200

master

B

slave

B

BM85

bridge

multiplexer

1 2 3 4

CPU A

primary

CPU B

standby

BP85

bridge

plus

BM85

bridge

multiplexer

1 2 3 4

SA85

network

adapter

= modem

bridge

modetasks 1

2

Hot Standby

configuration

5 8 40 (note 1)

Modbus plus network (up to 64 nodes)

Modbus plus network (up to 64 nodes)

Message Routing

180 890 USE 100 00 November 2004

Here are examples of routing between peer, master, and slave devices.

From To Routing Path

CPU A (primary) slave A 5 2 0 0 0

50 5 3 50 0 0

CPU C 25 2 0 0 0

SA85 (task 1) 25 30 1 0 0

slave B 25 4 2 0 0

200 25 4 3 200 0

CPU C SA85 (task 2) 30 2 0 0 0

slave B 4 2 0 0 0

200 4 3 200 0 0

CPU A (primary) 24 8 0 0 0

CPU B (standby) 24 40 0 0 0

100 24 5 3 100 0

SA85 slave B 4 2 0 0 0

150 4 3 150 0 0

CPU C 2 0 0 0 0

CPU A (primary) 24 8 0 0 0

50 24 5 3 50 0

Message Routing

890 USE 100 00 November 2004 181

If masters A, B, and C are programming panels such as the Modicon P230 they can

attach to various devices using direct, implicit, or MUX addressing or mapped

routing.

From To Address Routing Method

Master A CPU A (primary) 8 attach direct 8 0 0 0 0

slave A 72 attach MUX internal path

CPU C 252 attach implicit 252/10 = 25 2 0 0 0

50 50 attach mapped 0 3 50 0 0

200 200 attach mapped 25 4 3 200 0

Master B CPU C 2 attach direct 2 0 0 0 0

slave B 72 attach Max internal path

CPU A 248 attach implicit 248/10 = 24 8 0 0 0

200 200 attach mapped 0 3 200 0 0

50 100 attach mapped 24 5 3 50 0

Master C CPU A (primary) 248 attach implicit 248/10 = 24 8 0 0 0

CPU B (standby) 71 attach mapped 24 40 0 0 0

slave A 72 attach mapped 24 5 2 0 0

slave B 73 attach mapped 4 2 0 0 0

150 74 attach mapped 4 3 150 0 0

Message Routing

182 890 USE 100 00 November 2004

890 USE 100 00 November 2004 183

CPlanning Worksheets

Using The Worksheets

Overview Use these worksheets to plan the layout of your network and coordinate the ordering

of materials.

You can make photocopies of these worksheets as needed. Some copiers are

capable of expanding the size of your copies for greater detail.

For assistance with using the worksheets, refer to examples of completed

worksheets (see p. 101).

Node Planning

Worksheet

Use this worksheet to plan the device type, setup and configuration parameters, and

communications traffic at each node on your network. Use a separate worksheet for

each node.

Topology

Planning

Worksheet

Use this worksheet to plan the top-level layout of your network. Summarize each

nodeís address, device type, application, and site location. If you are using multiple

networks, this worksheet can show how they are interconnected.

Network

Planning Worksheet

Use this worksheet to detail the device type, length of trunk cable, tap, drop cable,

and method of labeling at each physical site location on your network. Each

worksheet has space for eight site locations. Use additional worksheets as needed

to describe your network.

Cable Routing

Worksheet

Use this worksheet to plan the individual sections of your network or to plan the

entire network, depending on the horizontal and vertical scales you want to use. You

can use multiple copies of this worksheet for your planning. Use a small scale on

some sheets to show local placements of devices and cables. Use a larger scale on

another sheet to show the overall network cable layout throughout your plant.

Planning Worksheets

184 890 USE 100 00 November 2004

Materials Summary

Worksheet

Use this worksheet to summarize your materials requirements prior to ordering. Be

sure to order cable in proper spool sizes to allow continuous runs between sites

without splices. If you are specifying a dual-cable network with RR85 repeaters, be

sure to order separate repeaters for each cable run.

Below is the node planning worksheet.

Modbus Plus Network

Node Planning Worksheet

Facility/Area:

Network Number:

Node Address:

Project Name:

Project Engr:

Maintenance:

Date:

Tel:

Tel:

1. Device:

Type Description Site Location

2. Application:

3. Setup Parameters:

4. Communications Originated:

Network Node

5. Communications Received:

Notes:

Priority Purpose Type of Communication Amount of Data Response Time NeededAmount of Data

Network Node Priority Purpose Type of Communication Response Time NeededAmount of Data

Planning Worksheets

890 USE 100 00 November 2004 185

Below is the notes worksheet for node planning.

Notes:

Planning Worksheets

186 890 USE 100 00 November 2004

Below is the topology planning worksheet.

Modbus Plus Network Topology Planning Worksheet

Facility/Area: Project Name:

Project Engr:

Maintenance:

First Entry:

Second Entry:

Third Entry:

Fourth Entry:

Legend: Node Number

Device Type

Application

Location

END End site of network section

Notes:

Date:

Tel:

Tel:

Planning Worksheets

890 USE 100 00 November 2004 187

Below is the notes worksheet for topology planning.

Notes:

Planning Worksheets

188 890 USE 100 00 November 2004

Below is the network planning worksheet.

Modbus Plus Network Network Planning Worksheet

Facility/Area: Project Name:

Project Engr:

Maintenance:

Notes:

Network Number:

Sheet:

Sites:Site:

1. Site Labeling: Name of site location:Plant site coordinates:Enclosure number:Panel label:Device label:Cable from previous site label:Cable to next site label:

2. Trunk Cable and Taps

Drop Cable, 2.4M/8FT, 990NAD21110:Drop Cable, 6M/20FT, 990NAD21130:

4. Device Type:Service access point connector:RR85 repeater:BM85 bridge multiplexer:BP85 bridge plus:Programmable controller (model no.):Host network adapter (model no.):Network option module (model no.):DIO drop adapter (model no.):TIO module (module no.):

Cable: A B

Of

To

Date:

Tel:

Tel:

Cable run from previous site, length:Service loop at this site (2 m/6 ft):Run length (sum of 2A and 2B):Cut length (multiply 2C times 1.1):Tap,990NAD23000: Termination jumpers installed in tap:

1A1B1C1D1E1F1G

2A2B2C2D2E2F

4A4B4C4D4E4F4G4H4I4J4K

3. Drop Cables3A3B

Planning Worksheets

890 USE 100 00 November 2004 189

Below is the notes worksheet for network planning.

Notes:

Planning Worksheets

190 890 USE 100 00 November 2004

Below is the cable routing worksheet.

Modbus Plus NetworkCable Routing Worksheet

Facility/Area:

Network Number:

Project Name:

Project Engr:

Maintenance:

Date:

Tel:

Tel:

Notes:

Sheet:

Sites:

A B C D E F

1

2

3

4

5

Scale: Horiz:

Cable:

To

Of

A__ B__

Vert:

Planning Worksheets

890 USE 100 00 November 2004 191

Below is the notes worksheet for cable routing.

Notes:

Planning Worksheets

192 890 USE 100 00 November 2004

Below is the materials summary worksheet.

Modbus Plus NetworkMaterials Summary Worksheet

Facility/Area:

Network Number

Project Name

Project Engr:

Maintenance

Date:

Tel:

Tel:

1. Network Devices

2. Trunk Cable and Taps

3. Drop Cables:

4. Labels:

5. Installation Hardware:

Notes:

6. Tools/Test Equipment

RR85 repeaterBP85 bridge plusBM85 bridge multiplexerprogcontrollerhost network adapternetwork option moduleDIO drop adapterTIO module

ModiconModiconModiconModiconModiconModiconModiconModicon

eacheacheacheacheacheacheacheach

MBplus trunk cableMBplus tap

ModiconModicon

reeleach

ModiconModicon each

990NAD21110990NAD21130

MBplus drop (2.4m/8ft)MBplus drop (6m/20ft)

paneldevicecableconnector

strain reliefs

each

990NAD2300

Description Part NumberQTYUsed

QTYSpare

QTYTotal

Unit ofMeasure

DateOrdered

DateReceivedManufacturer

Planning Worksheets

890 USE 100 00 November 2004 193

Below is the notes worksheet for material summary.

Notes:

Planning Worksheets

194 890 USE 100 00 November 2004

890 USE 100 00 November 2004 195

DInstalling Custom Cable Systems

At a Glance

Overview This appendix discusses installing custom cable systems.



Topic Page

Installing the Network Cable System 196

Tools and Test Equipment Required 197

Before You Start 198

Routing the Cable 199

Installing Connectors on Dual-Cable Runs 201

Installing Connectors with the Tool 202

Installing Connectors without the Tool 209

Grounding 216

Labeling 217

Checking the Cable Installation 218

Installing Custom Cable Systems

196 890 USE 100 00 November 2004

Installing the Network Cable System

Overview This topic describes how to install the network cable system without the use of

Modicon taps and drop cables. This method uses inline and terminating connectors

that are available from Modicon. It is intended primarily for the installer, but can also

be useful to the planner in estimating time and labor requirements.

You will be performing the following actions to install and check the cable.

! Route the cable (see p. 115) in accordance with the layout diagram.

! At each cable drop location, except the two extreme ends, connect the cable

signal conductors and shield to an inline connector.

! At the cable drop locations, at the two extreme ends, connect the cable signal

conductors and shield to a terminating connector.

! If the network node devices are installed, check that each one is grounded to a

proper site ground.

! Label the cable segments to assist in future maintenance.

! Inspect the cable run and check the cableís continuity before connecting it to the

network node device.


890 USE 100 00 November 2004 197

Tools and Test Equipment Required

Overview An installation tool (Modicon part number AS-MBPL-001) is available for installing

connectors on the cable. Use of this tool will make the installation much easier to

perform compared to the use of common hand tools only. It will also ensure positive

electrical contact between connectors and the network cable. Contact Modicon for

information about obtaining this tool.

The following additional tools and test equipment are required to install and check

the cable:

! wire cutter to cut the cable segments

! wire stripper or knife to remove the cable jacket

! flat screwdriver for assembling cable connectors

! voltameter for checking the cable continuity

If possible, avoid the use of cable pulling tools by laying the cable directly into

overhead troughs or raceways. This will minimize potential stretching or cutting

damage. If a pulling tool is used, follow the manufacturerís guidelines and avoid

excessive force in pulling the cable.


198 890 USE 100 00 November 2004

Before You Start

Overview Before routing the cable you should have a cable routing diagram that shows:

! site locations of network node devices

! routing paths of each cable segment

! cable segment distances and cut lengths

! list of materials required (length of cable, quantities of inline connectors,

terminating connectors, cable ties, adhesive labels, and other materials as

needed)

See p. 115 to prepare this diagram. If you cannot obtain such a diagram, you must

observe all the precautions described in this guide for physical and electrical

protection of the cable during installation.


Failure to provide proper physical protection of the cable can cause damage to the

cable conductors or insulation. Failure to provide proper electrical protection of the

cable can result in excessive interference induced from adjacent circuits. This can

cause degraded network performance.


CAUTION


890 USE 100 00 November 2004 199

Routing the Cable

Overview The figure below shows typical cable drops to several network node devices and a

service access point connector.

A horizontal runs secured in raceway or circuit

B shows a single-cable network cable run or each cable run (A or B) on a dual cable network

C one cable segment at each end drop

D two cable segments at each in-line drop

E strain reliefs

F network node device

G service access point

H end location

I inline location

J service loop

K inline connector (AS-MBKT-085)

L terminating connector (AS-MBKT-185)

A

IIH

F

G

F

C D

F

E

B

J KL

H


200 890 USE 100 00 November 2004

Refer to the figure above. Route the cable between the site locations of the network

node devices. Guidelines for cable routing are described below. For dual-cable

routing, follow these guidelines for each cable.

! Use a continuous length of cable between locations. Do not use any kind of taps

or splices.

! Two cable segments are routed to each inline drop location: one segment from

the previous drop, and one segment to the next drop.

! One cable segment is routed to the last drop at each end of the network.

! At each drop, allow sufficient cable for a service loop and strain reliefs.

! At each drop, provide a service loop to allow the cable to be connected and

disconnected from the network device without strain on the cable. A service loop

of 6 in (15 cm) minimum radius is adequate for most installations.

! Two cable ties are provided with each cable connector for use as strain relief. Use

one of these at each drop to secure the cable to a panel or other stable assembly,

to prevent the cableís weight from pulling on the connector. The other strain relief

will be used on the connector.

! Use additional ties as required to secure the cable from flexing or other damage

in areas of mechanical motion devices and traffic.

! If you are installing cables for a dual-cable network, the two cables should be

identified as cable A and cable B.

! Make sure that each cable is properly marked so that it can be positively identified

as cable A or cable B over the entire end-to-end length of the network.


890 USE 100 00 November 2004 201

Installing Connectors on Dual-Cable Runs

Overview At each inline device site, an inline connector (AS-MBKT-085) must be installed on

both cable A and cable B. At the two device sites at the extreme ends of the network,

a terminating connector (AS-MBKT-185) must be installed on both cables.

An individual connector is always wired to segments on the same cable only, never

to both cables. Cable A and cable B should remain independent through their entire

runs.

For example, a connector may connect to two segments on cable A. A separate

connector may connect to two segments on cable B. The same connector should

never connect cables A and B together.

Make sure to properly label each connector (A or B) so that it can be connected to

the proper port (A or B) on the node device when it is installed at the site.


202 890 USE 100 00 November 2004

Installing Connectors with the Tool

Overview A tool is available from Modicon (part number AS-MBPL-001) for installing the

connectors on your network cable. Use of this tool will ensure a positive connection

between the cable and connector. The tool is illustrated below.

If you are not using this tool, skip the instructions below. Go to p. 209.


890 USE 100 00 November 2004 203

Before You Start Make sure you have the proper type of connector for each point on the network

cable.

! Connector type AS-MBKT-185 (light grey) must be installed at the two end points.

Two connectors are contained in the Modicon kit with this part number.

! Connector type AS-MBKT-085 (dark grey) must be installed at each inline point.

One connector is contained in the kit with this part number.

The figure below shows the Modbus Plus connectors.

A install at end points

B install at inline points

C terminating connector AS-MBKT-185 (two per kit

D inline connector AS-MBKT-085 (one per kit)

You will need the following additional tools:

! electricianís knife

! wire stripper

! small, flat blade screwdriver

! ohmmeter with a low resistance range (0 ... 200 Ω)

You will also need to know which type of network device (type of Modicon 984

controller or other device) is to be installed at each point on the cable. The connector

wiring direction will depend on the type of device installed.

Overview of the

Connector Installation

Each connector requires seven steps:

! preparing the cable

! placing the connector into the tool

! determining the wiring direction

! placing the wires into the connector

! replacing the cap

! seating the wires and installing the cap screw

! completing the connection

1 2 31 2 3

BA

C D


204 890 USE 100 00 November 2004

Preparing the Cable

Follow the steps below to prepare the cable.

Placing the Connector into

the Tool

Step Action Result

Remove three inches (7.5 cm) of the

cableís outer jacket and shields as

shown in the figure below.

This will expose the cableís two signal wires

and drain wire.

Strip approximately 1/4 inch (6 mm)

of the insulation from the end of each

signal wire.

This will allow you to check wiring continuity

to the connectorís pins.

3.0 in (7.5 cm)

0.25 in

(6 mm)

Step Action

Select the proper connector (see p. 203). Remove the screw that secures the

connector cap, and remove the cap. Retain the cap and screw for reassembly.

Open the tool and place the connector into the cutout as shown in the figure below.

cutout

connector

in place

(cap removed)


890 USE 100 00 November 2004 205

Determining the Wiring Direction

The wires must be inserted into the connector in the proper direction for the type of

device to be installed at the site. The tool is labeled with the proper wire direction for

various network devices. Determine the wire direction for the device at the present

site.

The figure below shows an example of the wire direction for a Modicon 984-685 or

984-785 controller.

A wires in place (685/785 example)

B dress wires this side for 685/785

C dress wires this side for 385/485

D 1 inch (2.5cm)

If the device is not listed on the tool, the wires can be inserted from either direction.

In this case, choose the best direction according to the manner in which the cable is

routed on the device.

Placing the Wires into the

Connector

Follow the steps below to place the wires into the connector.

A

B

C

D

Step Action Comment

1 One cable (three wires) will be connected

to the connector at each of the two

extreme end sites. Two cables (six wires)

will be connected at each inline site.

2 Observing the proper wire direction, place

the wires into the slots of the tool as

shown above.

Make sure the white wires are toward

the handle end of the tool and the blue

or black wires are toward the pivot end.

3 When the white and blue or black wires

have been inserted, insert the bare drain

wires into the center slots of the tool.

Make sure the drain wires do not

contact any other terminal.


206 890 USE 100 00 November 2004

Replacing the Cap

Carefully replace the cap as shown in the figure below. Make sure the cap is properly

aligned to fit over the wiring terminals. Do not install the cap screw yet.

Seating the Wires and

Installing the Cap

Screw

Close the tool firmly to seat the wires into the connector terminals as shown in the

figure below. Close the tool completely against its stop tab. While holding the tool

closed, insert the cap screw through the hole provided in the tool and tighten it into

the connector with a screwdriver.

A Close tool firmly to seat wires in connector.

B Insert and tighten cap screw while holding tool.

cap in place(do not installscrew)

A B


890 USE 100 00 November 2004 207

Completing the Installation

Follow the steps below to complete the installation.

Check Wiring Continuity

Step Action

1 Open the tool, and remove the connector and cable. Locate pins 1, 2, and 3 of the

connector as shown in the figure below.

A continuity from white wires to pin 2

B continuity from bare wires to pin 1

C continuity from blue or black wires to pin 3

D trim wires after checking continuity

E pin view

F side view

Note: Wiring direction shown is for 984-685/785 controller.

2 Using an ohmmeter set to a low-resistance range, verify that direct continuity (zero

ohms) exists between each white wire and pin 2. Verify direct continuity between

each blue or black wire and pin 3. Verify direct continuity between each bare drain

wire and pin 1.

3 If an improper connection has been made, and you have already installed one or

both of the connectors at the two ends of the network cable, it is possible to read

either 60 or 120 ohms resistance between a blue, black, or white wire and its pin.

Make sure you have direct continuity (zero ohms) between wire and its proper pin

3 2 11 2 3

D

E

F

AA B C B C


208 890 USE 100 00 November 2004

What to Do Next Install the remaining connectors on the cable by repeating the steps in these

instructions.

After installing all of the connectors, follow the guidelines for observing the cable

precautions (see p. 216), and for labeling (see p. 217) the cable installation.

Check the entire cable installation (see p. 218) visually and electrically.

4 Verify that no continuity (an open circuit) exists between each white wire and each

drain wire. Verify that no continuity exists between each blue or black wire and each

drain wire.

Trim the Wires

Step Action

1 If continuity is normal, trim the excess lengths of wire so that they are flush with the

side of the connector. If continuity is not normal, repeat the installation procedure

with a new connector.

Install the Cable Ties

Step Action

1 Using one of the cable ties supplied with the connector, tie the cable tightly to one

of the connectorís side tabs. This will prevent damage in future handling of the

connector.


Step Action


890 USE 100 00 November 2004 209

Installing Connectors without the Tool

Overview If you are using the Modbus Plus connector installation tool (AS-MBPL-001), do not

follow the instructions below. Instead, refer to Installing Connectors with the Tool

(see p. 202).

If you are not using the installation tool, continue with the instructions below.

Before You Start Make sure you have the proper type of connector for each point on the network

cable.

! Connector type AS-MBKT-185 (light grey) must be installed at the two end points.

Two connectors are contained in the kit with this part number.

! Connector type AS-MBKT-085 (dark grey) must be installed at each inline point.

One connector is contained in the kit with this part number.

The figure below shows the Modbus Plus connectors.

A install at end points

B install at inline points

C terminating connector AS-MBKT-185 (two per kit

D inline connector AS-MBKT-085 (one per kit)

You will need the following tools:

! electricianís knife

! wire stripper

! small, flat blade screwdriver

! ohmmeter with a low resistance range (0 - 200 Ω)

You will also need to know which type of network device (type of Modicon 984

controller or other device) is to be installed at each point on the cable. The connector

wiring direction will depend on the type of device installed.

1 2 31 2 3

A

DC

B


210 890 USE 100 00 November 2004

Overview of the Connector

Installation

Each connector requires six steps:

! preparing the cable

! identifying the connector terminals

! connecting the wires

! inspecting the connection

! replacing the cap

! completing the connection

Preparing the

Cable

Follow the steps below to prepare the cable

Step Action Result

Remove 3 in (7.5 cm) of the cableís

outer jacket and shields as shown in

the figure below.

This will expose the cableís two signal wires

and drain wire.

Strip approximately 1/4 in (6 mm) of

the insulation from the end of each

signal wire.

This will allow you to check wiring continuity

to the connectorís pins.

3.0 in (7.5 cm)

0.25 in

(6 mm)


890 USE 100 00 November 2004 211

Identifying the Terminals

Remove the screw that secures the connector cap. Remove the cap to expose the

wiring terminals. Note the terminal numbers (1, 2, 3) marked on each side of the

connector.

SHARP EDGES

The connector terminals have sharp edges. Use caution when handling the

connectors.


CAUTION

top side

(covered removed)


212 890 USE 100 00 November 2004

Connecting the Wires

All wires will be routed into one side of the connector. The wiring direction depends

upon the type of device to be installed at the site, as shown in the figure below. If a

device is not listed, the wires can be routed into either side of the connector.

A cable to left for 984-385, 485

B wire to terminal

C cable to right for 984-685, 785

D press each white wire and blue or black wire fully into its terminal

E wire

F lay each bare drain wire into its groove

1

2

3

1 inch(2.5cm)

1 inch(2.5cm)

A B C

D

E

F

E


890 USE 100 00 November 2004 213

Note the wire color that will connect to each terminal. The white wire will connect to

terminal 1, the bare drain wire to terminal 2, and the blue or black wire to terminal 3.

Follow the steps below to finish connecting the wires.

The figure below shows how to connect the second cable (inline sites only).

A cable to left for 984-385, 485

B wire to terminal

C cable to right for 984-685, 785

Step Action Comment

1 To connect a white, blue, or black wire,

lay it across the top of its terminal with

the cableís outer jacket approximately

1 in (2.5cm) away from the connector.

Using the connector cap as a tool,

press the wire fully into its terminal.

When the wire is fully inserted, it will

bottom into its terminal as shown in the

figure above.

2 After connecting each wire, check

continuity between the wire conductor

and terminal.

Check this with an ohmmeter between the

exposed end of the wire and the terminal.

3 Lay the drain wire over terminal 2 (the

center contact area).

Do not allow the wire to contact any other

terminal. Make sure the drain wire is into

its groove in the connector body as shown

in the above figure.

4 If you are connecting an inline site,

refer to the figure below and connect

the second cable to the connector.

Use the same methods for connecting

and checking the wiring as for the first

cable.

112233

A B C


214 890 USE 100 00 November 2004

Inspecting the Connection

Visually inspect the completed connection:

! the wire colors are correct: white at terminal 1, bare at terminal 2, and blue or

black at terminal 3

! all wires are routed straight through the channels in the connector

! all wires are inserted completely into the channels in the connector

! the bare drain wire is not frayed and is not touching either terminal 1 or terminal 3

Replacing the

Cap

When all the wires are correctly placed in the connector, you can replace the

connector cap. Taking care not to dislodge any wire, fit the connector cap to the

connector body. Tighten the cap screw to secure the cap.

Completing the Installation

Follow the steps below to complete the installation.


Step Action

1 Locate pins 1, 2, and 3 of the connector as shown in the figure below.

A continuity from white wires to pin 2

B continuity from bare wires to pin 1

C continuity from blue or black wires to pin 3

D trim wires after checking continuity

E pin view

F side view

Note: Wiring direction shown is for 984-685/785 controller.

3 2 11 2 3

D

E

F

AA B C B C


890 USE 100 00 November 2004 215

What To Do Next Install the remaining connectors on the table by repeating the steps in these

instructions.

After installing all the connectors, follow the guidelines for observing the cable

grounding precautions (see p. 216), and for labeling (see p. 217) the cable

installation.

Check the entire cable installation (see p. 218) visually and electrically.

2 Using an ohmmeter set to a low-resistance range, verify that direct continuity (zero

ohms) exists between each white wire and pin 2. Verify direct continuity between

each blue or black wire and pin 3. Verify direct continuity between each bare drain

wire and pin 1.

3 If an improper connection has been made and you have already installed one or

both of the connectors at the two ends of the network cable, it is possible to read

either 60 or 120 ohms resistance between a blue, black, or white wire and its pin.

Make sure you have direct continuity (zero ohms) between wire and its proper pin.

4 Verify that no continuity (an open circuit) exists between each white wire and each

drain wire. Verify that no continuity exists between each blue or black wire and each

drain wire.

Trim the Wires

Step Action

1 If continuity is normal, trim the excess lengths of wire so that they are flush with the

side of the connector. If continuity is not normal, repeat the installation procedure

with a new connector.

Install the Cable Ties

Step Action

1 Using one of the cable ties supplied with the connector, tie the cable tightly to one

of the connectorís side tabs. This will prevent damage in future handling of the

connector.


Step Action


216 890 USE 100 00 November 2004

Grounding

Overview All three conductors of the cable (signal wires and shield) should remain isolated

from the panel grounding connection at each drop location. Grounding systems

should connect to the network device, not to the network cable.

If the network devices are installed, make sure each one has its grounding terminal

and frame properly connected to the plant grounding system. The grounding path

should be separate from paths used for motors, generators, welders, and other high-

current industrial devices.


890 USE 100 00 November 2004 217

Labeling

Overview After the cable is installed, label the cable segments for ease in future maintenance

of the network. Adhesive labels are available commercially for cable identification.

! If a cable layout diagram exists for the installation, label each segment in

accordance with the diagram. If a diagram does not exist, refer to the examples

in Elements of Network Planning (see p. 47) and prepare a diagram showing the

cable segments and method of identifying them for future service. Then label the

segments accordingly.

! Affix the labels to the cables at each network node drop. Place them at a point

visible to maintenance personnel.

! Complete the network installation labeling by properly labeling each siteís cabinet

or enclosure, device mounting panel, and device.

! Notify the person who will be responsible for future maintenance of the network

and deliver the network documents to that person. It is suggested you do a

walking tour with that person through the network sites to produce familiarity with

the network layout.


218 890 USE 100 00 November 2004

Checking the Cable Installation

Overview This section describes how to visually inspect the cable and check its end-to-end

electrical continuity.

Inspecting the

Cable

Installation

Inspect and ensure the following.

! The cable runs should agree with the physical and electrical protection

requirements (see p. 52).

! The cable runs should agree with the network cable routing diagram (see p. 48).

! Each inline drop site should have two cables, connected to one inline connector

(dark grey).

! The two end drop sites on each section of the network should each have one

cable, connected to a terminating connector (light grey).

! The cable direction (left or right) into each connector should be correct according

to the type of device to be installed at each site.

! Each connector should be tightly secured to its cable(s) by a cable tie.

! Adequate strain reliefs should be installed on the cable at each drop.

! All identification labels should be in place and properly marked.

Checking the Cable Continuity

These continuity checks are applicable to cable installations that use only the

components described in this appendix. These checks do not apply to installations

that use the tap and drop cable components (see p. 121). Before checking

continuity, disconnect all cable connectors from the network devices.

! At any connector, measure the resistance between pins 2 and 3 (signal pins).

Measure this at the connectorís external pins, not at its internal wiring terminals.

This should be in the range of 60 to 80 ohms, which includes the cable wire

resistance.

! At one end connector, connect a jumper between pin 2 (signal pin) and pin 1

(shield pin). At the other end connector, check for continuity between pin 2 and

pin 1. Continuity should be present.

! Leaving the meter connected as above, remove the jumper. Again check the

continuity between pin 2 and pin 1. It should be an open circuit.

! At the connector, check the continuity between pin 1 and the plant ground point

on the local site panel or frame. It should be an open circuit.

If your checks do not agree with these results, inspect the cable and connectors for

damage or miswiring and correct the condition.

890 USE 100 00 November 2004 219

Glossary

acknowledgment An LLC frame that indicates that a data has been received correctly.

address On a network, the identification of a station. In a frame, a grouping of bits that

identifies the frameís source or destination.

ASCII American standard code for information interchange. A digital coding of

alphanumeric and control characters as established by the American National

Standards Institute.

baud rate The speed of data transmission in serial data communications, approximately equal

to the number of code elements (bits) per second.

bit Binary Digit. The smallest unit of data, which can at any time be in one of two

possible states, represent by a value of 0 or 1.

bridge A device that interconnects two or more networks.

bridge

multiplexer

A Modicon device that interconnects a Modbus Plus network with up to four Modbus

devices or networks, or up to four RS232 or RS485 serial devices. See co-

processor.

bridge plus A Modicon device that interconnects two Modbus Plus networks.

A

B

Glossary

220 890 USE 100 00 November 2004

broadband A network communications method supporting multiple data transmission channels,

using frequency division multiplexing.

bus An electrical channel used to send or receive data.

carrier band A network communications method in which information is transmitted using a single

transmission channel. See broadband.

channel The communication pathway between two or more devices.

co-processor Bridge multiplexer models BM85S232 and BM85S485. These models contain a

user-defined application program that can independently control processes at their

four serial ports, accessing Modbus Plus nodes only as required.

coaxial cable A two conductor cable in which an inner conductor is the signal path and an outer

conductor is a shield. A dielectric separates the two conductors.

CRC Cyclic redundancy checking. An error detection method in which a sending station

computes a mathematical value derived from the frameís contents, and sends it as

an HDLC field in the frame. The receiving station recomputes the value as it receives

the frame, and compares it to the received vale. If the two values are equal, the

frame is assumed to have been received without error.

data frame An LLC frame containing data to be transferred between devices.

data link layer In the OSI model, the layer that provides services for transferring frames of data

between nodes of a network. Defined by the IEEE 802.2 standard. At this layer, a

sending device assembles data into a message packet with addresses and

information for error checking, handles tokens for accessing and information for

error checking, handles tokens for accessing the network, and sends the packet to

the physical layer for transmission. Its two logical entities are the MAC and LLC

sublayers. See MAC and LLC.

C

D

Glossary

890 USE 100 00 November 2004 221

DIO Distributed I/O. A Modbus Plus network that consists of hardware components that

are specifically designed for high-speed control of input/output devices at remote

sites in an industrial process. Each DIO network has one programmable controller

or one Modbus Plus network option module that operates as the master controlling

node on the network. The DIO network also has one or more DIO adapters, placed

at the remote plant site. Up to 64 nodes can be present on each DIO network,

exchanging messages during the passing of token frames.

download The transfer of a program from one device to another to another for execution.

drop cable A cable used to connect a networked node device to a tap on the trunk cable. Drop

cables are available in various lengths from Modicon. See tap.

duplicate frame A frame received twice because an acknowledgement was lost.

EIA Electronic Industries Association

end delimiter A field that defines the end of a message.

field A logical grouping of contiguous bits that convey one kind of information, such as

the start or end of a message, an address, data, or an error check.

frame A logical grouping of continuous bits for transmission; a message.

frame check

sequence

A code that is used to determine whether a frame was received correctly.

frame descriptor A part of the host computerís buffer structure that links transmitted or received data

frames to appropriate priority queues. Frame descriptors contain MAC frame

parameters, frame status, and pointers.

E

F

Glossary

222 890 USE 100 00 November 2004

global input A type of data input received by a node using peer cop data transfers. Nodes using

peer cop can be configured to receive up to 32 16-bit words of global input data from

each of up to 64 source nodes, up to a maximum total of 500 words. Incoming data

from each source node can be indexed into up to eight fields for delivery into

separate data destinations in the receiving node.

global output A type of data output sent by a node using peer cop data transfers. Nodes using peer

cop can be configured to send up to 32 16-bit words of global output data, which is

globally broadcast to all active nodes on the network. Destination nodes can be

configured to accept or ignore incoming data from specific source nodes.

HDLC High-level data link control. The part of the device that performs the protocols for

defining the beginning and end of a frame, synchronizing the frame between sender

and receiver, providing CRC error checking, and defining the portion of the received

information that is to be checked by the CRC.

host computer A computer which controls other computers and devices. In an industrial process

with networking, the host computer specifies the current requirements for the

operation of remote nodes, and is the destination for summary data reports about

the performance of the process.

IEC International Electrical Commission

IEEE Institute of Electrical and Electronics Engineers

ISO International Standards Operation

G

H

I

Glossary

890 USE 100 00 November 2004 223

LAN Local area network. An interconnection of devices in which data is transferred

without the use of public communications services. Modbus Plus is an example of a

lan for controlling and monitoring industrial processes.

layer In the OSI model, a portion of the structure of a device which provides defined

services for the transferring of information. See data link layer and physical layer.

LLC Logical link control. The part of the device that performs the protocols for identifying

users of the network and for providing reliable frame delivery. The LLC handles the

framing and checking of messages.

MAC Medium or (media) access control. The part of the device that performs the protocols

for sharing the network with other devices. The MAC handles the queueing and

transmission of outgoing LLC level messages, address recognition for incoming

messages, and resolution of access contentions.

map Manufacturing automation protocol. A network protocol that allows devices or cells

within an industrial environment to communicate with each other.

master A networked device which controls other devices to which it connects. It initiates

transactions, and schedules and transmits tasks to a slave device. See slave.

Modbus An industrial networking system that uses RS232 serial master-slave

communications at data transfer rates of up to 19.2 k baud.

Modbus II An industrial networking system that uses token-passing peer-to-peer

communications at data transfer rates of five megabits per second. The network

medium is coaxial cable.

Modbus Plus An industrial networking system that uses token-passing peer-to-peer

communications at data transfer rates of one megabits per second. The network

medium is shielded twisted-pair cable.

L

M

Glossary

224 890 USE 100 00 November 2004

modem Modulator/demodulator. A device that conditions digital data for transmission along

an analog signal path, or condition input signals received from the path for use as

digital data.

network The interconnection of devices sharing a common data path and protocol for

communication. On modbus Plus, the devices share in the passing of a common

token frame to gain sequential access for sending messages.

network option module

A hardware module that is mounted into a common backplane together with a

programmable controller, communicating with the controller over the backplane.

The module connects to the Modbus Plus network and provides the central point for

communication between the controllerís application program and the node devices

on the network.

node A device that has a direct point of access to a communications network. On Modbus

Plus, any device that is physically connected to the network.

OSI model Open systems interconnection model. A reference standard describing the required

performance of devices for data communication. Produced by the International

Standards Organization.

peer cop A method of peer-to-peer communication between networked devices in which data

is transferred as part of the passing of tokens between nodes. Each node passes

the token in the networkís address sequence, and can be configured to transmit data

in addition to the token. All nodes monitor the token passes, and can be configured

to extract data from them. Nodes are setup for peer cop transfers as part of their

initial configuration, and continue using peer cop as long as they are active on the

network. Four kinds of peer cop communication can be transacted during each

token pass: see global input, global output, specific input, and specific output.

N

O

P

Glossary

890 USE 100 00 November 2004 225

peer-to-peer communication

A communication between networked devices in which any device can initiate data

transfer. The method used by devices conforming to the OSI model. Also the

method used on Modbus Plus.

physical layer In the OSI model, the layer that provides the physical connection and signalling

means between nodes of a network. Defined by the IEEE 802.4 standard.

port The external connector on a device at which the network cable is attached.

protocol A set of rules used mutually by two or more devices to communicate.

repeater A Modicon Plus message frame, a group of five bytes that specify the address of the

devices in the message routing path.

RS232 An EIA standard that defines signal requirements and cable connections for serial

data communications.

section A contiguous grouping of cable segments, together with their node devices,

connected directly to form a signal path that does not pass through any repeater.

The minimum length of a section can be 10ft (3m), the same as one segment. The

maximum length can be 1500 ft (450 m). One section supports up to 32 nodes.

Repeaters can be used to join two sections for greater cable lengths and more

nodes. See segment.

segment The combination of: a continuous length of trunk cable connecting a pair of taps.; the

two taps; and the drop cables between the two taps and their node devices. One or

more segments form a section of the network. See section and tap.

serial port A communication port at which data is transferred one bit at a time.

slave A networked device which is controlled by another device. Slave devices do not

initiate data transactions. They respond to commands or requests initiated by a

master device. See master.

R

S

Glossary

226 890 USE 100 00 November 2004

slot time The amount of time representing the worst case time any station on the network

must wait for a response from another station. It is based upon the response time of

the networkís slowest station and the bus propagation delay.

specific input A type of data input received by a node using peer cop data transfers. Nodes using

peer cop can be configured to receive up to 32 16-bit words of specific input data

from each of up to 64 source nodes, up to a maximum total of 500 words. Nodes can

be configured to accept or ignore incoming data from specific source nodes.

specific output A type of data output sent by a node using peer cop data transfers. nodes using peer

cop can be configured to send up to 32 16-bit words of specific output data to each

of up to 64 destination nodes, up to a maximum total of 500 words.

splitter A passive device that allows a cable to be routed into multiple paths with essentially

equal signal amplitude in each path. Not used with Modbus Plus.

start delimiter A field that defines the start of a frame, occurring after the signal has been detected

and synchronized by the receiving node. See end delimiter.

system A set of hardware devices and their associated software capable of performing the

functions of information processing and device control without significant

dependence on other equipment.

tap A passive electrical device that joins segments of the trunk cable, or terminates the

trunk cable at its two end sites. It also provides a connection for the drop cable to

the node device at the tap site. See terminator.

terminator A resistive load placed at the end of a cable to prevent data signals from reflecting

back into the data path. The signals are terminated with the same impedance as the

characteristic impedance of cable system. On Modbus Plus, each tap contains a

terminating resistor with two jumpers. The termination is effective when the jumpers

are installed. The tap at each of the two ends of the cable section has its terminating

jumpers installed. The tap at each inline point has them removed. See section.

token In data transmission, a frame passed on a network that gives a networked device

that current authority to transmit.

token bus A network access method between two or more devices in which the procedure for

sending data is based upon the passing of a token for access to the network. See

token.

T

Glossary

890 USE 100 00 November 2004 227

transaction The complete and successful transfer of a message between networked devices.

trunk The main element of the cable system that interconnects the network nodes. On

Modbus Plus, the trunk cable runs directly between pairs of taps.

Glossary

228 890 USE 100 00 November 2004

CBA

890 USE 100 00 November 2004 229

AAC

applying power, 153

AC/DC model, 150

access

node, 31

address, 33

BP85 switch settings, 149

bridge multiplexer, 42

bridge plus, 39

consistent node addressing, 93

conversion, 174, 177

estimating latency fo a large network, 86

estimating throughput with peer cop, 80

factors for planning a Modbus Plus

network, 59

for best throughput on a single

network, 92

hot standby configuration, 20

planning for ring join time, 88

precautions for hot standby layout, 90

predicting node dropout latency time, 82

setting Modbus Plus address, 149

address, same

node uses, 30

application

typical network adapter, 25

application layout

with node access, 28

ASCII


on a Modbus Plus network, 94

Bbackplane

distributed I/O (DIO), 22

baud rate


BM85

address conversion, 177

application development tools, 45

silent master port, 178

support custom RS232 or RS485

application, 45

support model, 42

token holding time, 164

typical user-programmed application, 46

BM85 bridge multiplexer

connection, 25, 42

BM85 bridge plus, 26

BP85

dimensions (panel/shelf), 147

dimensions (rack mount), 148

mounting, horizontal or vertical, 146

mounting, rack, 146

network address switch settings, 149

setting the Modbus Plus addresses, 149

specifications (panel/shelf), 157

specifications (rack mount), 158


BP85 bridge plus

connection, 39

BP85 bridge plus module

queuing, 64

Index

Index

230 890 USE 100 00 November 2004

bridge

global data, 71

on a Modbus Plus network, 79, 98

using multiple bridges between

networks, 97

bridge multiplexer

ASCII, 43

message routing, 173

network planning, 49

on a Modbus Plus network, 13, 41, 94

RTU mode, 43

bridge plus, 39



bridge plus device


bus

MicroChannel, 24

Ccable

bus, 20

checking continuity, 218

connecting, 142, 152

connecting AC power, 150

connecting DC power, 150

connecting drop cable, 131

drop, 51

dual, 17, 20, 52

dual, length consideration, 53

dual-cable configuration, 36

estimating run distance, 54

inspecting installation, 218

install and check, 196

required lengths between nodes, 108

routing, 199

routing diagram, 124

single, 20

trunk, 128

cable installation

continuity, 136

drop cable, 122

example, 136

ground wire, 122

inspect, 135

jumper, 122

labeling, 134

node device panel ground, 122

overview, 122

tap, 122

tap grounding screw, 122

tools and test equipment required, 123

trunk cable, 122

cable routing

drop, 125

dual-cable network, 125

internal termination jumper, 125

network trunk cable, 125

cable routing guidelines, 52

cable routing worksheet, 110, 115, 190

cable segment


cable, minimum/maximum length, 17

cable, network

dual, 39

single, 39

clearance

BP85 (panel/shelf), 147

BP85 (rack mount), 148

communication path, 63

multiple networks, 96

configuration

RS232, 45

RS485, 45

configuration, linear

using RR85 repeater, 37

connecting AC/DC power, 150

connection

BP85 bridge plus, 39

grounding, 18

jumper, 18

network cable, 152

node, 18

tap, 18

Index

890 USE 100 00 November 2004 231

connector

inline, 196

installing on dual-cable runs, 201

terminating, 196

tools and test equipment for

installing, 197

controller


Ddata master path

in controllers, 63


data response time, 164

data slave path, 64


DC

applying power, 153

DC/DC model, 150

defining network components, 50

device interaction


dimensions (panel/shelf)

BP85, 147

dimensions (rack mount)

BP85, 148

DIO


on multiple networks, 95

servicing, 58

DIO drop adapter

servicing, 58

distributed I/O


distributed I/O (DIO)

backplane, 22

drop adapter, 22



servicing, 58

type of communication, 20

distributed I/O (DIO) drop adapter

servicing, 58

drop

cable, 48, 52

drop adapter


drop cable

connecting, 131

service access, 53

dropout latency time

predicting, 82

dual cable network, 39

cable routing worksheet, 115

network planning worksheet, 112

dual-cable

installing connectors, 201

length consideration, 53

dual-cable configuration, 36

dual-cable network

repeater placing, 37

Eelectrical interference

cable routing, 52

environmental requirements

cable routing, 52

error checking and recovery

node, 30

extending a Modbus Plus network, 12

Fflashes

network indicators, 154

frame

global data, 71

network layout, 54

Gglobal data

bridge, 71

frame, 71

network, 71

node, 71

token, 71

global database

on a single network, 92

Index

232 890 USE 100 00 November 2004

global database transaction, 29

global input

receiving data, 34

global output

transmitting data, 33

grounding, 216

connection, 18, 51

tap, 133

HHDLC

message format, 166

host-based adapter, 49

host-based network adapter


hot standby

precautions for layout, 90

II/O process


I/O servicing

network, 32

process, 32

identification

attaching port identification label, 156

impedance

terminating, 51

information requirements for planning a

Modbus Plus network, 59

inline connector, 196

inline site

connecting trunk cable, 128

inspecting

cable installation, 218

installation

network trunk and drop cable, 122

installing

connectors with tools, 202

connectors without tools, 209

interaction

between devices on a Modbus Plus

network, 60

interference

cable routing, 52

inter-network traffic

transactions that are less critical for

timing, 31

Jjumper

connection, 18, 51

Llabel

attaching port identification label, 156

labeling

cable installation, 134

cable segments, 217

latency

dropout time, 82

estimating for a small network, 84

formula for calculating node dropout, 83

length

cable, 52

drop cable, 51


length of a Modbus Plus network, 12

linear configuration


linear expansion

network configuration, 36

LLC

message format, 169

local device statistics, 69

MMAC

message format, 167

mapping

Modbus port, 44

master

device on a Modbus Plus network, 43

estimating latency for a large network, 86


Index

890 USE 100 00 November 2004 233

materials summary

worksheet, 110, 118, 192

message

HDLC, 166

LLC, 169

MAC, 167

message routing

for bridge multiplexers, 173

for host-based network adapters, 172

for programmable controllers, 172

routing, 172

message throughput

slow, 41

message transaction, 31

MicroChannel

bus, 24

Modbus Plus


defining network components, 50

joining networks, 39

MSTR communication, 67

MSTR instruction, 65

network performance, 57


overview, 12

sample communications across

networks, 98

statistics, 69

using peer cop, 33

Modbus Plus port 1 indicator

active network link, 142

Modbus Plus port 2 indicator

active network link, 142

Modbus port data path

loading effects in your application, 73

Modbus port mapping, 44

mounting, horizontal or vertical

BP85, 146

mounting, rack

BP85, 146

MSTR, 93

estimating throughput, 78

predicting response time, 76

type of communication, 20, 57, 65, 67,

69, 72, 74, 75, 76, 78, 91, 96, 98, 100

MSTR data path


MSTR function, 63

multiple networks

communication path, 96


guidelines, 95

peer cop, 95

Nnetwork

add node, 89

ASCII, 94

baud rate, 94


calculating rotation, 75

components, 50

configuration, 36

delete node, 89

device interaction, 60

document your layout, 102


estimating latency for a small network, 84

estimating throughput with MSTR, 78

factors for planning, 59

global data, 71

global database, 92

guidelines for a single network, 91

guidelines for multiple networks, 95

I/O servicing, 32

increase performance, 100

information requirements for planning, 59

linear expansion, 36


Modbus Plus, 14, 17, 20, 39, 98


MSTR instruction, 65

non-linear expansion, 38

Index

234 890 USE 100 00 November 2004

optimizing node count on a single

network, 93

performance, 57, 61

planning, 48


precautions for hot standby layout, 90

predicting MSTR response time, 76

predicting token rotation time, 74

prioritizing and compressing data, 94

remote programming on a single

network, 93

response time for a node on a Modbus

Plus network, 61

RTU, 94

security considerations for a single

network, 92

statistics, 69

using multiple bridges, 97

using peer-to-peer on a single

network, 91

network adapter

SA85, 24

SM85, 24

SQ85, 24

typical application, 25

network adapter (host-based)


network cable

connecting, 142

network components

defining, 50

network indicator

Modbus Plus port 1, 142

Modbus Plus port 2, 142

reading, 154

RR85 repeater, 143

network indicators

RR85, 138

network layout

cable routing, 102

frame, 54

installation materials, 102

labeling, 102

node requirements, 102

repeater, 54

setup parameters, 102

network option module


network option module (NOM)


network performance

transaction, 58



bridge plus, 49


dual-cable, 108

host-based adapter, 49

network option module (NOM), 49

node, 49

programmable controller, 49

repeater, 49

terminal I/O (TIO) module, 49

worksheets, 103

network planning worksheet, 110, 112, 188

node

access, 28, 31

add to network, 89


bridge plus, 39

calculating rotation, 75

connection, 18

consistent addressing, 93

data response time, 164

delete from network, 89

dropout latency time, 82

error checking and recovery, 30


estimating throughput with MSTR, 78

estimating throughput with peer cop, 80

global data, 71

grouping logically for increased

throughput with MSTR, 79

guidelines for a single network, 91



network layout, 52


network planning, 49, 100

Index

890 USE 100 00 November 2004 235

on a Modbus Plus

network, 12, 14, 16, 17, 33

optimizing count on a single network, 93


precaution for hot standby layout, 90

predicting MSTR response time, 76

predicting token rotation time, 74

response time on a Modbus Plus

network, 61


transaction requirements, 59

using same address, 30

node planning worksheet, 104, 184

NOM


non-linear expansion

example, 38

network configuration, 38

star configuration, 38

tree configuration, 38

Oouter shield wire

connecting, 132

Ppath type

for a Modbus Plus device, 63

peer cop


estimating throughput, 80

example, 35

global input, 34

global output, 33


performance example, 81

specific input, 34

specific output, 33

transaction, 33

transfer, 57, 80, 86

type of communication, 20

peer processor, 63

peer-to-peer


using on a single network, 91

physical damage

cable routing, 52

planning a Modbus Plus network

overview, 59

planning an application program, 62

point to point message transaction, 29

point to point transaction, 33

port identification label

attaching, 156

port mapping, 44

power

AC, 153

connecting AC/DC power, 150

connecting for the RR85 repeater, 141

DC, 153

process

I/O servicing, 32

program path


programmable controller


programming

remote, on a single network, 93

Qqueuing, 63

bridge plus message, 64

data transaction, 64

reduce or eliminate with multiple bridges,

97

Rreceiving data

specific input, 80, 86

recovery and error checking

node, 30

remote device statistics, 70

remote programming

on a single network, 93

Index

236 890 USE 100 00 November 2004

repeater

connecting power for the RR85, 141

network layout, 54



placed on dual-cable network, 37

RR85, 27, 37

RR85 horizontal mounting, 138

RR85 mounting dimensions, 139

RR85 network indicator, 143

RR85 network indicators, 138

RR85 specifications, 144

RR85 vertical mounting, 138

requirements for planning a Modbus Plus

network, 59

response time

for nodes on a Modbus Plus network, 61

ring

planning for joining, 88

rotation

formula for calculating, 75

rotation sequence

token, 28

routing

cable routing diagram, 124

message routing for bridge

multiplexers, 173

message routing for host-based network

adapter, 172

message routing for programmable

controllers, 172

trunk cable, 125

routing path field

in a typical message frame, 40

routing the cable, 199

routing through three networks, 40

RR85

connecting power, 141

horizontal mounting, 138

mounting dimensions, 139

network indicator, 143

network indicators, 138

repeater, 27, 37

specifications, 144

vertical mounting, 138

RS232, 25

configuration, 45

serial device, 42

RS485, 25

configuration, 45

serial device, 42

RTU


RTU mode


SSA85

network adapter, 24


section


security

considerations for a single network, 92

serial device

RS232, 42

RS485, 42

service access

drop cable, 53

shield wire

connecting, 132

signal wire

connecting, 131

silent master port, 178

single cable network, 39

cable routing worksheet, 115

network planning worksheet, 112

single network

ASCII, 94

baud rate, 94


global database, 92

guidelines, 91

optimizing node count, 93

prioritizing and compressing data, 94

remote programming, 93

RTU, 94

security considerations, 92

Index

890 USE 100 00 November 2004 237

selecting node address for best

throughput, 92

using peer-to-peer, 91

slave

device on a Modbus Plus network, 43




SM85

network adapter, 24


specific input

receiving data, 34, 80, 86

specific output

transmitting data, 33, 80, 85, 86

specifications

BP85 (panel/shelf), 157

BP85 (rack mount), 158

RR85 repeater, 144

speed process, design

token, 31

SQ85

network adapter, 24

star configuration


statistics

local device, 69

remote device, 70

Ttap

cable, 48, 51

connection, 18

drop cable, 51

grounding, 133

grounding screw, 127

installing trunk cable at end site, 129

installing trunk cable at inline site, 128

mounting, 127


trunk cable, 51

terminal block I/O


terminal block I/O (TIO)

servicing, 58

terminal block I/O (TIO) module, 23

terminating connector, 196

terminating impedance


terminating resistor, 51

test equipment

for installing connectors, 197

required for cable installation, 123

throughput

estimating with MSTR, 78

estimating with peer cop, 80

increasing by grouping nodes

logically, 79

selecting node on a single network, 92

slow, 41

timing

data response, 164

read/write transaction, 165

TIO


servicing, 58

TIO module, 23

token

bridge plus operation, 39

designing for speed process, 31


global data, 71


holding time, 162


predicting node dropout latency time, 82

rotation, 67, 70, 74, 75, 76, 80, 91

rotation sequence, 28

rotation time, 164

transmission, 72, 98

tools

for installing connectors, 197, 202

required for cable installation, 123

topology planning worksheet, 106, 186

required cable length, 108

traffic

inter-network, 31

Index

238 890 USE 100 00 November 2004

transaction

across the bridge, 31

global database, 29


peer cop, 33

point to point, 33

point to point message, 29

statistics, 69

transferring, 72, 84, 86, 92, 100

transaction requirements

for planning a Modbus Plus network, 59

transfer

peer cop, 57

transmitting data

specific output, 80, 85, 86

tree configuration


trunk

cable, 48, 50

trunk cable

connecting, 128

connecting wires, 130

inline site, 128

jumper, 128


tap at end site, 129

tap at inline site, 128

UU/I


user interface (U/I)


Wwire

connecting outer shield wire, 132

connecting signal wire, 131

worksheet

cable routing, 103, 110, 115, 190

materials summary, 103, 110, 118, 192

network, 112

network planning, 103, 110, 188

node planning, 103, 104, 184

topology planning, 103, 106, 186